I had many old collections that I didn't get back, but I usually finished a collection before getting another one. The only one that I was looking for was the one that I was working on. I was on the next to last puzzle, but I gave up trying to get it back and I wasn't going to download it again, because I was almost finished with it.
Since I have many bars, I haven't been keeping track of them. So I may have gotten bars for the collections that I lost. I get many more bars completing the puzzles in a collection, than I spent to get the collection.
I have never tried to get the old version back . I agree with your intention of completing your current collection before getting the latest version. I'm in the US.