Ernest -

My base document is a reprint of a 1896 S.S.Stewart catalog reprinted by Mugwumps back in 1973 in which there are no 4-string banjos listed. A variety of 20th century ones do surface on E-Bay that do not appear to demonstrate the quality of construction of what I've seen from the 1890's. That's not to say that Stewart didn't produce an occasional 4-string banjo during this period but if they did so it would be an extremely rare banjo. What does your look like?