Ok so I know this is possible because I've done it before, but it doesn't seem to work now.
So my friend and I are working on a mod, he is the owner am a contributor. I've done some edits to his work-he does the exterior and I do the interior. When he updates his mod, it just updates the uploaded mod (that is hidden of course). Yet when I upload my changes to the mod, it always uploads as a new mod rather than updating the one that I am a contributor to.
How we used to do it was that we would just choose the same file and add our changes when we did something, and upload the archive to steam. It would say 'getting details on published files' and the title would appear and then it would update.
Now it still says 'getting details on published files' but no title comes up after that and it uploads as a new mod.
Any help would be appreciated.