Its my understanding that week 53 only occurs when there are 53 start days in a calendar year. Like 53 Saturdays if that is when you start your week. Same thing for weeks that start with a Friday or Sunday start. Happens at a lot of timeshares and at most of them you only pay for that week if it will occur that year.
Each timeshare company has their own policy as to MF's for week 53 or usage. Some just keep it dark and use that week for major refurishments to the units or as a rental.