Hi Kim,
Yes, I only allow single use of the token and it will decrease after the survey has been completed so that part works as expected. But I've since found out that it will allow you to submit many partial surveys until one is completed. I'm not sure how that's happening as I've just tested that if I save the survey (to resume later), I will get back to the same partially completed one whether I click on the invite link or the saved link (from resume email). I think it's when you don't save the survey but the partial response is actually saved although you can't access it again later, that's all.
I'll have to test this further. But if what I've described is correct, LS shouldn't keep the partially done survey if user has not clicked resume later since there's no way they'll be able to get back to that survey so that record is 'orphaned'. I'll update after testing the different scenarios.
Cheers,
Karen