Has there been a categoric "Party Locking means no changing/finding new companions post Act1"?
Or is everyone jumping on this because Larian have previous in DOS2 and stated they want you to choose out of the initial companions which ones to go forward with?
Well, it's more that we've been asking clarifications about that statement since the EA started and we never really got one.
So yeah, a lot of people are defaulting to DOS 2 as reference since it matches to T what they are describing here.
