First and most obviously, it's different for every SP. They don't all follow the same schedule.
Second of all, there's no way for them to prove it, you would just have to take their word. If they showed you someone's results it would expose the their real names, birthdate, etc. If they hid that info, then they could just show fake results and pass it off as whoever you're asking about and you would never know.
Thirdly and most importantly, it's none of your fucking business. If you can't accept the risks of this hobby, then do everything safe or just stay home and jerk off. You and you alone are responsible for your own safety, not them.
When's the last time *you* got tested? Post your results here for all of us to see.