From https://koha-community.org/manual/latest/fr/html/erm.html#import-from-kbart-label I believe Print isbn is imported in 020 in MARC21 This is not the standard way to map Kbart to MARC21. Even if I don't know if there is is an official mapping, you can take as an example the mapping of this provider : print isbn is going to 776z https://marc-openedition.readthedocs.io/en/latest/marc21.html#books for unimarc it should be 452y https://marc-openedition.readthedocs.io/en/latest/unimarc.html#books you can also see this example from Springer : https://metadata.springernature.com/api/metadata?eisbn=978-3-030-54602-1&format=MARCxml They add a 776$i "Printed edition" before the 776$z And the mapping used by Clarivate in Alma https://knowledge.exlibrisgroup.com/Content/For_Content_Providers/Enrichment The same logic applies to ISSN : print ISSN should be in 776$x in Marc21, 452$x in unimarc
I wrongly described those references, which are not, strictly speaking, mappings between KBART and MARC, but rules for describing e-resources in MARC. Anyway, I still believe it would be better not to put print isbn and issn in 020 or 022 field