I'm still not entirely sure. I think Reddit's had the same issue with some of its feed when subreddits went from private to public, so if even they struggle wit

I'm still not entirely sure. I think Reddit's had the same issue with some of its feed when subreddits went from private to public, so if even they struggle with it, then it might not be entirely straightforward. Not even sure RSS readers like Thunderbird have features to deal with duplicates like that.