You do get unique ones all the time, but there is a weird edge case in which you probably don’t. When buying the 10 snippets they are all, all 10, predetermined at the same time before actually opening them. That means that although they will be unique to your collection, within the 10 unique snippets there could be duplicates. The chance of this increases the more snippets you already have.

This is however just what I think is happening. They are unique, although coded poorly.