I’ll carefully analyze your suggestions for our next releases.
The Spotify message is not related to territorial restrictions. Putting it shortly, Concertmaster database wasn’t pre-checked; it checks the availability of each recording in real-time, after user’s request. That's why Concertmaster keeps showing recordings that don’t exist at all on Spotify.
This is brilliantly implemented so hats off for that. It's something I always had on my backlog of personal projects but never got round to doing, but you've managed it far better than I could ever have hoped to.
One thing that would noticeably improve the experience for me: Being able to sort a given series of works by opus/[equivalent catalogue number] or date. It seems at the moment the only sorting method is alphabetical, which is often not particularly helpful (for example, as someone else noted, when 10 appears before 1).
I'm studying the sorting thing. Opus/catalogue number: not so easy because the data comes from sources that treat this information as strings. But I can think of a text parser, for example. Year of composition: doable.