Thank you again for the reply.
I have always driven the 922A with 50 watts from the same exciter (TS-850S)
I have not seen any decrease in output power in the last 5 years. It puts out 1.3 kw on 75 meters which is as advertised.
Perhaps you are correct in your questioning of the value of the shunt on the meter changing value.
That would be the best scenario of all possible outcomes that I can think of.