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.
After some continued research on the TWdB, I've come to realize that the "88" in the serial number has likely nothing to do with the palm tabulator.
The 88 is for an extra character count due to more keys (44) versus the more standard 42 or 43 keys and similarly some examples with a 92 in the serial number corresponds to 46 characters. So there isn't a designator in the serial number for a palm tabulator.
See: <br /> - https://typewriterdatabase.com/1961-royal-fp.22586.typewriter<br /> - https://www.reddit.com/r/typewriters/comments/1kg820b/just_bought_this_typewriter_for_10_at_a_charity/<br /> - https://amsterdamassassin.wordpress.com/2018/12/16/typecast-my-royal-fp-steampunk/
KoponewtPelicram ❤️ Slug Goblin 3 points4 points5 points 3 hours ago (3 children)Do you know what's the serial number on that? Some manufacturers had special models mostly for export purposes with extra keys. For example Royal 11 is a 10 with extra keys, Underwood No. 46 is a 5/3/6 with extra keys. Remington No. 9 is an 8 with extra keys.
via https://old.reddit.com/r/typewriters/comments/1jgg4kh/royal_kmm_extra_column_of_keys/miyumvn/