We have a C15 to which we have added circa 100 Tidal albums over the last few weeks.
Upon signing up to Roon, the overview menu shows 825 albums, of which about 25 are resident on my Macbook Pro. The remainder are all Tidal albums, the majority of which I am not familiar with.
This 825 shows up whether or not the C15 is turned on. Any of these albums will play via MS200 endpoints. Clearly Tidal has a vastly larger library than 825 albums, so how has Roon selected these particular albums?