[Koha] Confusion between 099 and 942 field in UNIMARC and comparison with MARC21

[Mathieu Saby]

Hi
I believe there is something wrong in UNIMARC default framework (https://github.com/Koha-Community/Koha/blob/main/installer/data/mysql/en/marcflavour/unimarc/mandatory/unimarc_framework_DEFAULT.yml )

We have 2 fields for "local" data (specific to Koha) at biblio level : 099 and 942
And the same pieces of information are present in subfields of both fields :
- 099$x and 942$0 (Number of issues => biblioitems.totalissues)
- 099$s and 942$s (Serial record => biblio.serial)
- 099$t and 942$c  (Koha item type => biblioitems.itemtype)

I suppose it is an error, because it makes no sense... And note that the 099 field in UNIMARC framework is called "local dates", so it should not contain information about item type or number of issue.
Do you think we could remove safely from the default templates 099$x, 099$s, 099$t ?  I don't know if those values may be harcoded somewhere in the code.

Moreover, it could be interesting to reduce the discrepancy between MARC21 and UNIMARC, so I wondered if we could get rid of 099 in UNIMARC.
So I searched for the equivalent of 099$c (Koha biblio creation date => biblio.datecreated) and 099$d ( Koha biblio modification date => biblio.timestamp) in MARC21, but I was surprised to find no place in 942 or elsewere to store  those pieces of information. Have I missed something ?

Regards,
Mathieu Saby
Université Cote d'Azur