The variation in content of these mirror sites is sufficiently explained by this quote from the top of the ca one:
All the functionality of the original Mutopia site has been restored, and the piece count will continue to increase as projects are restored from the Wayback Archive. Full restoration (~2200 pieces) is anticipated to be completed in April. New developments will be posted here in this space. Paul From: Mats Bengtsson <matsboxergr...@gmail.com> To: <lilypond-user@gnu.org> Cc: <enquir...@mutopiaproject.org> Sent: 31/03/2022 15:05 Subject: Re: Mutopia? On 2022-03-31 11:38, Silvain Dupertuis wrote: Would it be that everything is now on this page: https://www.ibiblio.org/mutopia/ Sincerely That seems like an extremely outdated site "Latest additions ... 2010...". Rather, try https://scores.omet.ca/ with the alternative interface https://mutopia.omet.ca/, see https://www.mail-archive.com/mutopia-discuss@mutopiaproject.org/msg00535.html Having written this, I happened to find http://eremita.di.uminho.pt/mutopia/ this is unmaintained but seems to contain contributions up to 2019, whereas https://mutopia.omet.ca/ says "Latest additions ... 2018...". I include a Cc: to the maintainer of https://mutopia.omet.ca/, perhaps it's possible the use the full database from the http://eremita.di.uminho.pt/mutopia/. /Mats