diff --git a/gui/src/app/Project/ProjectDataModel.ts b/gui/src/app/Project/ProjectDataModel.ts
index 23eab70..c9c048e 100644
--- a/gui/src/app/Project/ProjectDataModel.ts
+++ b/gui/src/app/Project/ProjectDataModel.ts
@@ -92,7 +92,9 @@ const isProjectBase = (x: any): x is ProjectBase => {
 
 export enum DataSource {
   GENERATED_BY_R = "generated_by_r",
+  GENERATED_BY_STALE_R = "generated_by_stale_r",
   GENERATED_BY_PYTHON = "generated_by_python",
+  GENERATED_BY_STALE_PYTHON = "generated_by_stale_python",
 }
 
 type ProjectMetadata = {
@@ -104,7 +106,7 @@ export const isProjectMetaData = (x: any): x is ProjectMetadata => {
   if (!baseObjectCheck(x)) return false;
   if (typeof x.title !== "string") return false;
   if (
-    x.dataSource !== undefined && // allow undefined for backwards compatibility
+    x.dataSource !== undefined && // undefined = manually edited or unknown provenance
     !Object.values(DataSource).includes(x.dataSource)
   )
     return false;
diff --git a/gui/src/app/Project/ProjectReducer.ts b/gui/src/app/Project/ProjectReducer.ts
index e791c27..1a0d04f 100644
--- a/gui/src/app/Project/ProjectReducer.ts
+++ b/gui/src/app/Project/ProjectReducer.ts
@@ -71,8 +71,12 @@ const ProjectReducer = (s: ProjectDataModel, a: ProjectReducerAction) => {
     }
     case "commitFile": {
       const newState = { ...s };
-      if (a.filename === ProjectKnownFiles.DATAFILE) {
-        newState.meta = { ...s.meta, dataSource: undefined };
+      const newDataSource = confirmDataSourceForCommit(
+        s.meta.dataSource,
+        a.filename,
+      );
+      if (newDataSource !== s.meta.dataSource) {
+        newState.meta = { ...s.meta, dataSource: newDataSource };
       }
       newState[a.filename] = s.ephemera[a.filename];
       return newState;
@@ -102,4 +106,25 @@ const ProjectReducer = (s: ProjectDataModel, a: ProjectReducerAction) => {
   }
 };
 
+const confirmDataSourceForCommit = (
+  currentSource: DataSource | undefined,
+  editedFile: ProjectKnownFiles,
+): DataSource | undefined => {
+  if (editedFile === ProjectKnownFiles.DATAFILE) return undefined;
+  if (
+    editedFile === ProjectKnownFiles.DATAPYFILE &&
+    currentSource === DataSource.GENERATED_BY_PYTHON
+  ) {
+    return DataSource.GENERATED_BY_STALE_PYTHON;
+  }
+  if (
+    editedFile === ProjectKnownFiles.DATARFILE &&
+    currentSource === DataSource.GENERATED_BY_R
+  ) {
+    return DataSource.GENERATED_BY_STALE_R;
+  }
+
+  return currentSource;
+};
+
 export default ProjectReducer;
diff --git a/gui/src/app/Project/ProjectSerialization.ts b/gui/src/app/Project/ProjectSerialization.ts
index 1912466..c9cfd10 100644
--- a/gui/src/app/Project/ProjectSerialization.ts
+++ b/gui/src/app/Project/ProjectSerialization.ts
@@ -112,7 +112,7 @@ const loadMetaFromString = (
   json: string,
   clearExisting: boolean = false,
 ): ProjectDataModel => {
-  let newMeta = JSON.parse(json);
+  const newMeta = JSON.parse(json);
   if (!isProjectMetaData(newMeta)) {
     throw Error("Deserialized meta is not valid");
   }
diff --git a/gui/src/app/pages/HomePage/HomePage.tsx b/gui/src/app/pages/HomePage/HomePage.tsx
index c407296..1682782 100644
--- a/gui/src/app/pages/HomePage/HomePage.tsx
+++ b/gui/src/app/pages/HomePage/HomePage.tsx
@@ -5,6 +5,7 @@ import useMediaQuery from "@mui/material/useMediaQuery";
 import StanFileEditor from "@SpComponents/StanFileEditor";
 import TabWidget from "@SpComponents/TabWidget";
 import TextEditor from "@SpComponents/TextEditor";
+import { ColorOptions, ToolbarItem } from "@SpComponents/ToolBar";
 import { FileNames } from "@SpCore/FileMapping";
 import { ProjectContext } from "@SpCore/ProjectContextProvider";
 import {
@@ -16,6 +17,7 @@ import Sidebar, { drawerWidth } from "@SpPages/Sidebar";
 import TopBar from "@SpPages/TopBar";
 import DataPyWindow from "@SpScripting/DataGeneration/DataPyWindow";
 import DataRWindow from "@SpScripting/DataGeneration/DataRWindow";
+import { unreachable } from "@SpUtil/unreachable";
 import {
   FunctionComponent,
   useCallback,
@@ -26,7 +28,6 @@ import {
   useState,
 } from "react";
 import SamplingWindow from "./SamplingWindow/SamplingWindow";
-import { ToolbarItem } from "@SpComponents/ToolBar";
 
 type Props = {
   //
@@ -124,30 +125,51 @@ const LeftView: FunctionComponent<LeftViewProps> = () => {
   );
 };
 
-const DataEditor: FunctionComponent<{}> = () => {
+const DataEditor: FunctionComponent<unknown> = () => {
   const { data, update } = useContext(ProjectContext);
 
   const dataIsEdited = useMemo(() => {
     return data.dataFileContent !== data.ephemera.dataFileContent;
   }, [data.dataFileContent, data.ephemera.dataFileContent]);
 
+  const dataSourceDesc: undefined | { msg: string; color: ColorOptions } =
+    useMemo(() => {
+      if (dataIsEdited) return undefined;
+
+      switch (data.meta.dataSource) {
+        case undefined: {
+          return undefined;
+        }
+        case DataSource.GENERATED_BY_PYTHON: {
+          return { msg: "data.py", color: "info.main" };
+        }
+        case DataSource.GENERATED_BY_R: {
+          return { msg: "data.R", color: "info.main" };
+        }
+        case DataSource.GENERATED_BY_STALE_PYTHON: {
+          return { msg: "a prior version of data.py.", color: "warning.main" };
+        }
+        case DataSource.GENERATED_BY_STALE_R: {
+          return { msg: "a prior version of data.R.", color: "warning.main" };
+        }
+        default:
+          return unreachable(data.meta.dataSource);
+      }
+    }, [dataIsEdited, data.meta.dataSource]);
+
   const dataMessage: ToolbarItem[] = useMemo(() => {
-    if (data.meta.dataSource === undefined || dataIsEdited) {
+    if (dataSourceDesc === undefined) {
       return [];
     } else {
       return [
         {
           type: "text",
-          label:
-            "Data is generated by data." +
-            (data.meta.dataSource === DataSource.GENERATED_BY_PYTHON
-              ? "py"
-              : "R"),
-          color: "info.main",
+          label: `Data generated by ${dataSourceDesc.msg}`,
+          color: dataSourceDesc.color,
         },
       ];
     }
-  }, [data.meta.dataSource, dataIsEdited]);
+  }, [dataSourceDesc]);
 
   const onSetEditedText = useCallback(
     (content: string) => {
diff --git a/gui/test/app/Project/ProjectReducer.test.ts b/gui/test/app/Project/ProjectReducer.test.ts
index b868146..6996783 100644
--- a/gui/test/app/Project/ProjectReducer.test.ts
+++ b/gui/test/app/Project/ProjectReducer.test.ts
@@ -145,6 +145,12 @@ describe("Project reducer", () => {
       expect(result[ProjectKnownFiles.DATAFILE]).toEqual(
         result.ephemera[ProjectKnownFiles.DATAFILE],
       );
+    });
+    test("Saving data.json clears data source", () => {
+      expect(initialState[ProjectKnownFiles.DATAFILE]).not.toEqual(
+        initialState.ephemera[ProjectKnownFiles.DATAFILE],
+      );
+      const result = ProjectReducer(initialState, commitAction);
       expect(result.meta.dataSource).toBeUndefined();
     });
     test("Save action does not save non-chosen files", () => {
@@ -157,6 +163,55 @@ describe("Project reducer", () => {
       const result = ProjectReducer(initialState, commitAction);
       expect(result.ephemera).toEqual(initialState.ephemera);
     });
+    test("Saving data generation script updates status on data it generated", () => {
+      const pairs = [
+        {
+          source: DataSource.GENERATED_BY_PYTHON,
+          newSource: DataSource.GENERATED_BY_STALE_PYTHON,
+          file: ProjectKnownFiles.DATAPYFILE,
+        },
+        {
+          source: DataSource.GENERATED_BY_R,
+          newSource: DataSource.GENERATED_BY_STALE_R,
+          file: ProjectKnownFiles.DATARFILE,
+        },
+      ];
+      pairs.forEach((p) => {
+        const initial = {
+          ...initialState,
+          meta: { dataSource: p.source },
+        } as any as ProjectDataModel;
+        const commit = { ...commitAction, filename: p.file };
+        const result = ProjectReducer(initial, commit);
+        expect(result.meta.dataSource).toEqual(p.newSource);
+      });
+    });
+    test("Saving data generation script does not change status for data.json it didn't generate", () => {
+      const pairs = [
+        {
+          source: DataSource.GENERATED_BY_PYTHON,
+          file: ProjectKnownFiles.DATAPYFILE,
+        },
+        {
+          source: DataSource.GENERATED_BY_R,
+          file: ProjectKnownFiles.DATARFILE,
+        },
+      ];
+      const sources = Object.entries(DataSource);
+      pairs.forEach((p) => {
+        sources
+          .filter(([, value]) => value !== p.source)
+          .forEach((s) => {
+            const initial = {
+              ...initialState,
+              meta: { dataSource: s },
+            } as any as ProjectDataModel;
+            const commit = { ...commitAction, filename: p.file };
+            const result = ProjectReducer(initial, commit);
+            expect(result.meta.dataSource).toEqual(s);
+          });
+      });
+    });
   });
 
   describe("Updating sampling options", () => {