The one on the right seems to have been made with a heavier impression from the stamping machine. Other than that, I don't see a difference.

Some hot stamp dies were made with a separate denomination piece that fit into the center of the die. That let them make different denomination chips without having to generate a new die for each. Sometimes the center part was not seated properly on a reorder and the number was stamped heaver. I would speculate that might be what you are seeing... a chip from a reorder, but not a different design.