New South Wales
Mission 3 introduces the restriction to choosing which Schematics to bring along as that is the first case where there is a limitation. If you were meant to remove the existing Schematics from play when you get new ones, the rules would be quite clear on that.
Alternatively, just look in the main manual:
MvM rules: Schematic Cards wrote:
Schematic Cards are powerful Yordle-
specific abilities that require
Team Gears to activate. At the start
of each Mission, each player
chooses up to two Schematics to
bring to the Mission. The player can
choose any Schematic unlocked so
far, but only Schematics associated
with the Yordle they are playing as.