NOTATIO

To anyone who uses the RISM catalogue regularly: I am not seeing all available online sources I request when I do a search on their catalogue, just a few.

For example, a simple search on W. A. Mozart/Sonatas/Piano/Autograph Copy does not even show all those available at IMSLP, which are taken from the various libraries cataloged by RISM. The Autograph copy of the first sonata KV 279 is found in a library in Cracow, and can be seen at IMSLP but is not found in the list.

Is a complex search necessary to find all the sources?

In my experience, the quality and usefulness of RISM has greatly degraded since their last big update (I think it was last year?).
Sometimes I even fail to find something I know I had browsed on their system, reason for which I always keep a permalink list of their pages for future re-use.