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In the post 1987 period (or even starting with the 1984 Earl Scruggs models) Gibson often assigned serial numbers (FONs?) by banjo MODEL. Various models had their own serial number "system". The one you gave is clearly intended just for the RB model line. Style 3 reissues usually started with "3". Granada numbers had a different format from Scruggs models, etc.
Mac - since I was not the original buyer/owner I cannot answer your question - nor did I ask the seller about any known modifications.
Typically though, when acquiring a 'supplemental' banjo, I completely disassemble it to take precision measurements and note identifying numbers and logos, locate any problems (including neck re-sets and re-fitting upper co-rod washers), clean, reassemble and re-setup. This then becomes the first few pages of the banjo's log records that grow in length over the years as I note my own tinkerings, adjustments, tonal changes etc, etc.
After checking my notes yesterday about this supplemental banjo, I posted above what I found "as-is" at its first disassembly.
Personally, I think it sounds great. It obviously hadn’t been played for some time. I went over it, new strings, head tension, truss rod tweak, bridge. Frets are a bit high, but Snap, Crackle and Pop. The figured maple is really nice, and simple inlay is nice. I also like the headstock. I just think it’s kind of a rare bird with all the right parts.