The trail to the well defined American longrifle likely had several forks starting at the imported German gun; some builders made new guns the same as they were trained to build in Germany, some guns were restocks that looked like the donor gun, some were restocks with new ideas, some guns were all new with a blend of old and new ideas, and some guns were all new in concept and parts. They were likely not built at identical times, but the time spans overlapped. They all followed a certain sense of acceptable contemporary fashion, guided by a firm hand of acceptable cost, in addition to practical ideas about how the guns had to be used.
The same thing happened with guns dominated by English, French, and Dutch ideas, and they cross pollinated up and down the coast over a period of only 60 or 70 years; which is remarkable, I think, considering the difficulty of travel and the press of simply making a living in that time.