@Roslyn0
Any reservation that is more than 28 days long, automatically goes on the "long term cancellation policy". That happens for every host, regardless what cancellation policy they have set for shorter reservations. This happens because as you point out, one can't easily replace such a reservation on short notice, and it is not fair to the host to have someone cancel that close to the date of arrival and get a full refund. So the way the long term cancellation policy works, is that once a guest books, then if they cancel, regardless of when they cancel, you will always get paid 100% of the first month's payment. THey can get the remainder of the reservation refunded if they give 30 days' notice, but they cannot get the first month refunded.
See info on long term cancellation policy here:
https://www.airbnb.com/home/cancellation_policies#long-term