I'm creating my 9th sample from a certain mailing list, and I don't seem to be able to add any more sampling criteria at this point to exclude earlier samples. I need to be REALLY sure that I'm not accidentally sending someone the same email survey invitation twice, so when I create sample 9, I have been using sampling criteria to exclude sample 8, sample 7, sample 6, and so on. But now Qualtrics won't let me add any additional sampling criteria. Any ideas?

Also--it seems like there must be a better, more efficient way to do this in the first place than manually excluding every previous sample. Maybe something with the transaction details…? I’m a little nervous about relying on those for a real survey unless I get solid confirmation first that it’ll work, and I couldn’t seem to find anything about it on the support pages. Which is all to say: I’d happily take any and all guidance on how to accomplish this goal, whether or not it involves excluding every single prior sample manually. Thanks in advance!