Salvete! Welcome to the Community. :)
Question: I have selected USMARC/MARC21 as my installation's native format. This serves nicely when I perform Z39.50 queries against many USMARC/MARC21 sources. On the other hand, when I perform Z39.50 queries against UNIMARC sources, I don't get properly formatted results even though I have set-up those sources (origins) as UNIMARC in koha.
I understand that both standards encode the same more-or-less information, differently. Therefore - if I understand correctly - koha would have to request from an UNIMARC-only-capable source that they return UNIMARC-formatted results, and koha would need to map them - if and as possible - to the native format of my installation, i.e. USMARC/MARC21.
Apparently this doesn't happen. Is it normal?
That is very normal. MARC21/UNIMARC is an either or standard selection. You may have MARC21 or you may have UNIMARC. To my knowledge, you may not have both. That said, when this last came up, I can see the point of wanting to be able to run both in parallel if you absolutely MUST have both. Suggestions for how to do that are here: http://koha.1045719.n5.nabble.com/Software-error-td5114149.html Cheers, Brooke