Hi Nicole,
Unfortunately, we do not currently have a way to limit past dates, as often times other customers may need to enter in historical data. I can log this as product feedback for you, and I also recommend you posting this in the Ideas Tab for others to vote on adding such a feature!
In the meantime, I recommend adding help text reminding requesters to not place a request for a past date, or you can add a check box for requesters to confirm that they are NOT submitting a request for a past date.
Hope this helps!
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Madeline Stalnaker [Designation]
Lead Client Success Advisor
Cvent
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