Wrong CYS id of IMGT

[kxz18]

When I tried to number the light chain 'SDIVMTQATSSVPVTPGESVSISCRSSKSLLHSNGNTYLYWFLQRPGQSPQLLIYRMSNLASGVPDRFSGSGSGTAFTLTISRLEAEDVGVYYCMQHLEYPLTFGAGTKLEL' in IMGT scheme, it gives me the 1-st CYS at (24, ' '). However, according to the IMGT official website, the 1-st CYS should be at (23, ' '). I'm wondering why this would happen. Also, the conserved TRP and 2-nd CYS are also shifted to (42, ' ') and (105, ' ') which should be (41, ' ') and (104, ' ').

Here is my code:

>> from anarci import number
>> seq = 'SDIVMTQATSSVPVTPGESVSISCRSSKSLLHSNGNTYLYWFLQRPGQSPQLLIYRMSNLASGVPDRFSGSGSGTAFTLTISRLEAEDVGVYYCMQHLEYPLTFGAGTKLEL'
>> numbering, chain_type = number(seq, scheme='imgt')
>> numbering

[kxz18]

By the way, I use conda to install ANARCI by:

conda install -c bioconda anarci

by conda list | grep anarci I get the version information as follows:

anarci 2021.02.04 pyhdfd78af_0 bioconda