This is all really interesting and good to know. I’m guessing Depeche Mode fall in the category of “no 80s compilations”, it now looks like Mute is becoming more difficult to license with the lack of Yazoo on the Yearbooks.Yeah, there's any number of points in the process where the request can get turned around. I know there were at least 11 sign off points/signatures required in the LOCAL office of one of the major labels in Australia (won't say which one) before any request was put to the overseas label or local artist management.
But 22 years in the music industry, I can tell you in no uncertain terms that there would only be a handful of actual artists who would see a compilation request. (I'm trying to think of one where I know for sure the artist has signed off and I think Kate Bush is the only one I know, and that's only for the portion of (and because it is) her catalogue she owns herself, she doesn't get a say at all about the rest).
The artist-management relationship is usually such that the trust is put in the manager to make the right choices for the artist and they're left to bat them back with a yes or a no on the artist's behalf based on whatever conversations they've had with them. It may be that an artist has said to their management "no branded comps" (Abba) or "no alcohol related/drinking themed comps" (a couple of artists I can think of, including a very famous artist with a well-publicised alcohol dependency issue) or "no 80s-themed albums" (PSB) or "always approve as long as it's Track 1, Disc 1" (Queen, and for a while John Lennon's estate until they realised they kept missing out on placements to Queen and settled for Track 1, Disc 2) and the management knows what to approve and what not to based on those meetings/chats. They don't bother the bands or singers with this shit, it's paperwork and that's what the manager gets paid to deal with.