So this one has no rhyme or reason. Colson started using side stands in 1938 on their high end bikes. As you've noticed all the '41 ads show sidestands not only one the top models but at least down to second tier as well. Most, if not all, of the Imperials and Clippers I've come across have side stands while it seems a lot of the Firestone bikes have drop stands. I can't see where this would have been an economic advantage. The Firestone bikes were typically a cheaper bike so maybe they just used up the remainder of their dropstands on the Firestone products and when they ran out started using side stands. All pure conjecture on my part but one way to test this theory is to compare serial numbers and see if only the later bikes have dropstands? Of course with the passage of time its impossible to know if the stands on some bikes were not changed out over the years. Those are my ramblings on the subject...