Rental availability that spans over a year?

I've seen a few properties in which someone has listed a unit as being available for over a year with a note that says something like "availability may vary." Can anyone tell me anything more about these listings? Are they from the property itself or a perhaps an owner that a great deal of flexibility?

"Availability Varies" postings indicate the owner has a floating week but has not yet reserved a week with the resort. A person interested in renting would contact the owner and ask if the owner is able to reserve the specific week they are wanting. The owner would have to check with the resort to see if there is still availability for those dates prior to engaging in a rental transaction.