Lets look at my own mod for instance. If I suddenly got bored of it and packed it in, then I found a year later in my inbox a question from someone asking to do the rest of the work but still credit me, would I be bothered? Not in the least, I would be flattered someone had taken the bother to do something with it. Heck I'd love it, I'd get to play my mod and explore things and places I didnt make and didnt know the solution to. Then I'd probably pile in with more effort to work as a team. If however that person was putting the mod out as their own and claiming the ownership of the hundreds of meshes etc I'd made. Well I'd be furious and hammer them on every forum. I could possibly prosecute, but that would be precious and daft. Lex non curat de minimis.
If I found some of my stuff in another mod without someone crediting me and I contacted them and they said they had tried to ask, made every effort and were desperate. I'd tell them not to worry, Ive been there and making the same thing over again is an absolute pain. Modders are generally more generous and more charitable than folk give them credit for.
back in the beginning of Mesogea I rounded up loads of mods with free to use but credit me conditions on them. After years of work I made a right old boo boo and lost the read me file where I had listed them. I worked like heckers to get all the details in the read me again but I am sure there will be the odd article in there that I will have missed in the credit list. So I stuck an end bit to the credits stating "If your work has been included in this mod and you find you are not credited please contact me as the omission was not intentional but owing to a genuine error on my part. I will ensure that full specific credit is then given and included in all updates. Thank you for your understanding."
Now if someone said point blank they didnt want their work included in another mod, I wouldnt have bothered with it in the first place.
Just be reasonable and ensure you give credits (and dont delete old files without reading them, especially when they just say "new document" on them. ooops.