box sets always pose a challenge because if you ask 3 people how to manage it, you get 3 answers (not tech, but how to view - some see each album in a set as separate, someone else as one, etc)
And sorry to say, any boot leg items, would be a roll of the dice. The info comes from publishers to start. There is no standard. Your best bet is to play with the settings, and when you see the result you like, run with that.
Sometimes flexibility, means things need more hand holding to see what you like.
this thread discusses outright that Apple isn't set up for box sets, and the work around is of your own devising. In short you're probably asking it to do something never designed. I often send in many apple.com/feedback suggestions about how to improve. The key - offer a solution, and not only the complaint or problem.
I have a couple of artists and some of their work, that their box sets don't play well in Apple. It's unfortunately an area that could improve. But often in these cases because as I said earlier, you have varying expectations, the work around is for you to enter parameters yourself to get the outcome you want to see. That's what I did and solved 90% of mine.
A box set - for example my opinion - can be a complilation of covers the artist did (that's know under other artists names) is a huge area of disagreement how to handle. I personally think a box set is still at the root at the DISC level and not the box itself. The box is an external housing (again to me). I'm illustrating there is no one way and probably no matter how Apple "fixed" this in a future upgrade, we'd still find something not to our liking.
I'm the first one to not give in, but more and more are want our apps, devices etc to do SO much, and hold so much data, and for long periods of time we have progressed and even generations pass. I'm saying that the flexibility is really the better choice, instead of Apple fixing it, and putting you into something you risk not liking (and can't adjust).
Take a deep breath, take a break, and experiment a little. I suggest if you find something that work, post your reply with a few screen shots to this post and help others!
Naming Discs in Box Set - Apple Community