Do the rules around getting up from subdual still count if there is a duel or spar going on and the winner forgot to move from Subdual to Sparring? Additionally, is it true that there are penalties given to a subdued player when they get up and if so, what are they?

A character that has been subdued suffers temporary AC and movement penalties; if it's some kind of fair tournament or duel, the non-mechanical restrictions are more between the players involved (but there needs to be a certain level of trust between the players that it won't become a problem DMs need to look into). If it's a gangland beatdown or an ambush in the Underdark, follow the rules we put out.