Reservations that were made on the booking channel and completed, i.e., checked out, before the booking channel was connected with Guesty will not be counted as part of the nights limit you set for the relevant listing in Guesty.
For example, if you set a 60 night limit for a listing that existed on the booking channel before it was connected with Guesty, and that listing already "used up" 20 nights before connecting, the annual limit for that listing will remain 60 after the connection process is complete.
To comply with local laws and make up for the difference in the year the listing was connected to Guesty, you can set a 40-nights limit for the connection-year and keep the 60-nights limit for future years.