As stated, the other simmers would have to own the same aircraft otherwise it’s up to model matching.
As a PC Simmer, we have other options open to us though. I use AIG for model / livery matching.
As for tail number, no you would never see another simmers tail number as it just shows up as a white block, regardless of model matching efforts.
The livery itself may show up as the same, or another livery associated with that model (if you’re using a default livery then chances are pretty good it would match up otherwise it will use one in its library).
I hope that helps.