I have had similar experience with CD/SACD metadata, including title, artist and artwork. I don’t know what source PSA is using to search for metadata. My old Oppo used Gracenote (and advertised as such in it’s display) and it resolved virtually everything I played.
With my DMP, when I see unresolved title/artist or artwork on my playlist, it’s not hard to highlight it and enter/update the title and artist data. For artwork, I open a window to Discogs and search for the specific release that I own. (check label, format, and release date, since the artwork can differ for different editions). Then one can copy the artwork image on the upper left and paste it into a folder local on your PC. Then, you click the unfound artwork image on your PS playlist, browse to your local folder (your playlist browse function remembers your local folder), highlight/open the just downloaded artwork file, and click upload on your playlist. Your playlist then is updated and ‘remembers’ the metadata for that item in your collection. Unfortunately, for an item with no metadata initially found, you don’t have the tracklist either. I’ve not had the energy to enter the whole tracklist and timings. OTOH, the DMP does find the tracklist/timings on the actual CD/SACD table of contents and so, does display the playing track/timing on the DMP display.