JDM is right on the money and in fact I would push that number out to about 12-14 at least because I've held them in my hands. I'm a HUGE fan of the work that guy was doing, very American and very folk-art. At least half that I've seen personally were dead plain but were indeed signed, and then there are a few that have been well photographed over the years and are more elaborate/well-decorated. I believe there are probably @ another 5 to 10 that are the same guy but are not signed. I believe very strongly that Stoffel Long had some form of association with Jacob George Jr., the Jacob George whose work also has survived via quite a few examples (published) and a number of which very closely resemble the work of Long. My suspicion is that Jacob George Sr, who was a gunsmith and general smith (proven by period records) trained them both - I believe Long and George Jr. were approximately contemporaries but I have not had the time to dig into this much further.
Dakota60 I would in turn be extremely interested in any genealogical information which you may have turned up regarding Stoffel Long, i.e birth and death dates, tax records, census etc. as all of this information is very helpful when trying to map out where and when and with whom a particular smith may have worked. Please post here any verifiable information which you may have uncovered as I promise you it will be very well-received!