Can anyone tell me when the classic banjo style was defined and what event, book, or musician marks that event.   Did the 6 and 7 string banjo predate the style, was it ever an accepted part of the style or was it part of the minstrel style?

The seven string does not seem to have been a big part of American banjo history although Dobson  was making 7 string banjo by 1877 (Rob Mackillop) and I have a Dobson 7 string flush fret which has a seven string tailpiece patented 1881 imported…