Ah, ok - I very much doubt that it"s original to Fenaroli, as it makes no sense!. The figures always conform to the key, with accidentals appearing when notes are foreign to the key signature- as you would expect. The only legitimate accidental is in bar 11. A slash through a figure means that it is to be raised, not flattened.
The difficulty with the example that I quoted, is that the figures don"t reflect what"s happening in the music and vice versa.
It"s odd, as the wiki article on the rule of octave gives the same figures, though that example is in G major, so it"s easier to see how that mistake could be made - it"s still redundant though. The mistake with the slash 5 figure is repeated there also. It appears that the example that I quoted is a direct transposition of the wiki one, mistakes and all!