My understanding is that Harley Davidson, over the years, contracted with a number of other builders besides Davis to build their bicycles.
I would suggest that what increases the value of Davis built Harley Davidson bicycles, as with many things, is their rarity. I've been told by
respected collectors and historians that two of the key features that Harley Davidson insisted be part of frames that were to become
Harley Davidson models were a split bottom bracket / crank hanger with left and right side bearing-race clamp screws, and signature HD forged
drive sprockets. Two of the companies that I was told built frames for Harley Davidson were Shelby and Columbia. Attached to their frames were
a pair of rain gutter fenders with the front fender incorporating riveted on tail-end side skirts, extended handlebars on men's models. Also on certain
men's models were tubular "tanks" with a tapered tail end and a removable styled forward end piece for battery access. On a restoration project I once competed on a 1917 men's model which, as found, had a badly bent drive sprocket that I replaced with a near perfect reproduction version that, after nickel plating and polishing, could not be distinguished from an original. So as not to misrepresent the bike to the buyer I disclosed the fact
of the reproduction sprocket when I presented the bike for sale but I doubt anyone could have ever discovered the sprocket was not original.