1) Backsets- our mortise locks have a 2 1/4" backset. It is possible for an old mortise lock to be different.
2) Tongue colors- we have received some mortise locks with "orange" tongues. SOLUTION: warranty and replace
3) Sticking- usually caused by incorrect faceplate installation. SOLUTION: remove and reposition faceplate
4) Knob won't retract the latch- a) wrong spindle size spinning in lock, or knob, or b) broken lock SOLUTION: if spindle is not spinning in lock, or knob; replace the lock