How do instances work in raids?

[DiosAspur]

I understand that each player has a new instance every week for each raid, this way people can't abuse farming boses like in dungeons. The question is, if, for example, a player who killed DBS, can another day join another raid group that has also killed DBS or a higher boss? Or he will just appear in another instance

[Disktrasa]

You cannot join another raid, if they summon you, you cannot se them and they cannot se you, once you kill a boss you get a unique ID to that very run, you CAN however create a raid or if that very same people who was in your original raid make a group to continue on DBS, but pugs in general don't want to join those raids for obvious reasons.