I would suggest 1 guest canceling because the cottage didn't have an additional night be taken as a consideration. Guests reasons for canceling maybe something else but they didn't want you to focus on their reason.
IIt worked you are focused on what can you do?
You have multiple cottages. You have clearly stated that. Sometimes we Hosts, me included, forget guests had enough brain power too get an Airbnb account, find my listing make a reservation and payment and then cancel early enough to get a refund. That suggests if just dates were the issue when it is not easy to find similar it takes maybe 5 minutes to send an email to you and ask. can you help?.