Prah: If they didn't fix it back then, they will probably never fix it.
I don't doubt it has been going on for quite a few years, but like I said, I imagine it is down to manually entering the necessary entries in a database, and not really a bug as such ... unless the bug is related to manually entering the entries into the database, but then I am sure we would see a lot more of this issue if that were the case.
I suspect it is a case, where GOG are short staffed enough at times that things either get missed (skipped) or the person doing them doesn't exactly know what they are doing.
It probably wouldn't take much to fix each instance, but they would need to assign a dedicated person, and also need a list of such games, as it would be a nightmare to discover these instances. Perhaps we could help out by providing a list, though if they are constantly struggling with staff numbers and or skill sets, then likely it will never be a priority.