Typically, if I need to use a particular benefit, I'll at least click through any obvious links to make sure that I understand how the benefit works and what the restrictions are. The Wyndham website, for the "Late Check-out," has a drop-down box that has a pretty clear "More Information" link. Clicking that has the first few words of "Offered upon request and subject to availability"

Based on that, I'd read additional details before counting on that benefit (and then making an angry post when that "subject to availability" gets invoked.) Especially with Wyndham generally having more lower-end properties, status benefits are going to not be as consistently enforced or even known by hotel staff. Any loophole that leaves the definition of availability up to the hotel should be seen as though the benefit is nothing more than a courtesy if you get a willing property.

By the way, "how full the parking lot is" isn't an indication of how full the property is, or will be that evening. People may be out and about during the day, thus having rooms occupied but not having their vehicle at the hotel at that precise moment. People may also get to the hotel a number of different ways (Uber/Lyft, maybe a charter bus, etc.) The only reliable way is to check on the website and see if they're still selling that room type for availability for that evening. Of course, that still doesn't account for those that may have asked for late check-out before you, nor does it account for whatever the property thinks it can allow for late check-out, if at all, since Wyndham doesn't require any litmus test for the hotel's availability.