age (month) help

I had a water heater on the last inspection with a “M” Any idea of the month?

Kenmore. 40 Gal.
Serial # M91535798

State
Kenmore
Reliance
Maytag
Apollo
1st letter = month, A=Jan, M=Dec, etc., letter i is not used
2nd and 3rd digits = year
Example: J01-128999 = September 2001

Gary

OK,… didnt know “i” was not used. That makes sense now. THANKS Gary.