I think this is more just people misunderstanding how the Wondrous Tails book itself worked. That is, they thought that a particular duty would be tied to a particular sticker, or that using retry would remove a sticker. This is not the case. Thus, retry doesn't swap stickers around or remove one, but just lets you redo a task you've already done to earn another sticker, while counting another duty you've yet to do as "Done" to account for the stickers you already have.

So of course you wouldn't be able to use it once you have all 9 seals.