chain_sequence.tsv references accessions in the IMGT-HLA that are now deprecated. Here are examples of accessions that are deprecated (keys) and the accessions I have been using in place (values):
{"HLA00022": "HLA00023", "HLA00508": "HLA00509", "HLA00867": "HLA14828"}
As a result, the sequence in the table is wrong for HLA00508.