When in doubt, look for that information while in your car. That is the best way to get the most accurate status of a site and how many stalls may currently be available (or if the site is, as sometime happens, temporarily closed). Well, the best way is to speak with someone who is actually there charging of course, but that's a little harder to do
To be fair, there are times when a site has just been finished that you will see mention of it here on TMC (or in other social media) that a site is open before it even shows up in the car's navigation system. The lag between open and it showing up in-car is narrowing these days (usually, but not always).