Today I ran the FSDT Live Update. Is it safe to say that it brought all my FSDT airports and GSX up to date.
Yes, that's what it does. It updates everything installed in one go.
If so how can I tell what versions I have of each airport and GSX.
The reason of having a Live Update that can update everything you have installed in one go, it's precisely that you don't have to wonder which "version" you have. The whole concept of a scenery "version", in fact, it's basically useless, with such kind of Live Update.