Originally Posted by The International
[Latin, In fact.] In fact, in deed, actually.
This phrase is used to characterize an officer, a government, a past action, or a state of affairs that must be accepted for all practical purposes, but is illegal or illegitimate. Thus, an office, position, or status existing under a claim or color of right, such as a de facto corporation. In this sense it is the contrary of de jure, which means rightful, legitimate, just, or constitutional. Thus, an officer, king, or government de facto is one that is in actual possession of the office or supreme power, but by usurpation, or without lawful title.
So based on the above definition of de facto from a legal dictionary, I would say that using a fastpass after the expiration is 'de facto usage', meaning is illegal (or to use a more accurate term 'against the rule') but tolerated. Not that allowing usage after expiration means that the rule no longer exists. The upcoming enforcement of fastpass return times will be 'de jure'; rightful and legitimate as it complies with the rule of fastpass return times as it exists in 'Disney's Rule Book'.
Remember many states have laws in existence 'de facto'. Laws against swearing in front of ladies or not being able to ride an elephant down the street on a Sunday. Laws that are NOT enforced but remain laws just the same, and if some lady wanted to have a person arrested for dropping the 'F-bomb' in front of her, the police would probably have to do it. There was a recent case involving adultery where the wronged spouse successfully won a large settlement from her husband's mistress based on a 19th century law. One that 'de facto' was never enforced, but still on the books.