If you have park tickets that are for a certain number of days and you know how many days are left, then after you tap into the park, you can look at the ticket information on
MDE, which will show days remaining. That's the only for-sure way I know of, although there is a location pointer on MDE, but I'm pretty sure that every single person in your party would have to have their own MDE account and look at this location pointer, which would show that they were in the park. However, I have no proof that this is correct.
If you're booking a BG and try to add members of your party that MDE thinks are not tapped in (even though they are tapped in), just forget about them for the moment and add everyone who MDE will allow to be added. Then, after you get a BG, go to a GET CM and they will add your other person/people for you as long as that person/those people are with you. You can't use this method as some kind of workaround to try to get people on your BG who aren't in the park. For one thing, I'm pretty sure that a CM can tell from your ticket media when you tapped in--even if your MDE account doesn't know.
But this might not even be a problem for you. It is something that's happened to a lot of parkgoers, but hardly all of them.