I once tried to compile a list of Konami's LC internal catalogues but there were too many holes (I suspect they weren't used just for albums) to I stopped, didn't though nobody would care.
But seeing there is a barcode/jan field, another one for these internal IDs would add nice, and I think it would be useful to help filling label holes. More interesting that pre-tax prices at least.
Maybe it could be used/extended for internal pressing IDs / matrix codes (see
this) too.