follow up reply:
After some additional research on the typewriter database, the YY = 92 (where the serial number is of the form: FP[P,E,S]-XX-YY-#######, where XX is the platen length and YY is for other special features) indicates that the machine has 46 character keys (and thus 46*2=96 glyphs on the slugs). There are also examples of YY=88 with 44 keys versus the standard 42 or 43 keys.
This means that your machine has a few extra keys not found on their standard keyboards at the time.