If we are going to get pedantic about what is "medieval" as oppossed to "Renaissance" then the late medieval run into early renaissance period - there is no hard an fast rule about when one ended and the other started. Also plenty of medieval practices continued into the renaissance period. It is likely that a dance written down in 1490 already existed at that date rather than being composed then.

However I agree that you should tell them that you are using a dated source - I am not sure it will make much difference to them whether the dance was written down in 1490 or 1410. Last time i was involved in a "medieval fair" I was being paid to Morris dance!