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/

reply:

I've been looking at the typewriter database and have been able to discern the fact that the designator YY=88 seems to indicate that an FP had a Royal HH-like palm tabulator, 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.

I can't help but wonder what the YY = 92 indicates on Martyn's machine.

https://reddit.com/r/typewriters/comments/1kg820b/just_bought_this_typewriter_for_10_at_a_charity/

For a second, I thought perhaps the "88" in the serial number was a designator for the palm tabulator, but one of the other two in the database doesn't have that option (visually), though the single picture (of 5853) looks like it may have broken off or been removed on that example: - https://typewriterdatabase.com/1960-royal-fp.1241.typewriter - https://typewriterdatabase.com/1961-royal-fp.5853.typewriter

If you upload some additional photos of yours to the database, perhaps we can puzzle out what the "88" designator means if it's not the palm tabulator functionality?

The E on FPE means "elite" or 12 characters per inch. The "13" indicates a 13 inch wide platen. The raw serial number seems to indicate it was made in 1960: https://typewriterdatabase.com/royal.72.typewriter-serial-number-database