Chainsaw Repair

I would imagine your control switch has been changed at some point with a later one.
My serial number is 127656770
Mine has the + sign in a circle at the start of the number not at the end like yours. Whats also strange is yours is read from looking from the centre of the saw out whereas mines read from looking" from the outside of the saw in" so almost like yours has been stamped the wrong way if that makes sense. Im over the pond in the U.K but cant imagine it would be stamped the opposite way around.
You clearly have an early model as the very first only had 8 digits not 9 hence why the x is listed at the start of the serial number.

The technical bulletein from stihl is dated march 1994 listing the changes that will be made so the 10mm-12mm change was around about that era.