This is a difficult problem. I licensed a game that had no credits in the game or the packaging but did have a not quite complete list in MobyGames, so what I did was list more complete credits in the store descriptions of my version, butafter several people complained about their titles, I removed all the titles (mobygames asked me about that and noted some studios like Valve do that) and still someone complained that they did all the work in their section and no one else should even me mentioned, and that they were losing out on jobs because recruiters would check mobygames and see it didn't match what they said and they were going to hire a lawyer. So I ended up removing all my credits and anyone who wants to see or add their name can go to mobygames (imdb now has game credits too).
Which doesn't help your situation except to say sometimes you try to do the right thing and people don't appreciate it (and on the other side of the coin it is true that often studio heads don't give proper credits or even use them as reward/punishment). I do like the idea of listing everyone who made any contribution no matter how small (and I try to also list any third-party assets, e.g. unity asset store packages, open source libs...), and now I like the idea of industry crediting stands like they have in tv/film, which has some inflexibility but at least you can point to a set of rules that you abided by, and IGDA was working on crediting standards for a while.
One other thing I do to avoid misunderstandings or worse is not accept or incorporate any contributions to my projects unless there's a clear contractual arrangement, i.e. I'm paying them. I've made a few exceptions, such as friend or a loyal customer providing some translations, but I've encountered some well-intentioned people who offer to collaborate and overvalue their contribution (my favorite is someone on facebook who said "I'm an artist and I think I can help you" and he drew a picture of my front end menu with a multiplayer button added).