Pickle Rick - S3-E3
Continuity mistake: When Pickle Rick is waiting for the elevator to arrive, he is standing on the first floor tile directly in front of the elevator door. Once the elevator door opens, he is suddenly standing several floor tiles away from the door.
Answer: C-137 is the dimension they came from since the pilot. After C-137 is Chronenberg'd, Rick and Morty travel to a replacement dimension that we haven't found out the designation of (although they may have moved dimensions again). The "original" Jerry, Beth, and Summer are still on C-137 though.
Bishop73