Of course, all these items are true and I was aware of them. My point is that comic artists who are hardware fans, as R. del Villar seems to be, tend to draw the latest and hottest machinery. The Bill Barnes planes appeared in pulp magazines around 1934-1935. While it's quite possible del Villar kept copies in his swipe file for a decade, it's more likely that he was working from copies just a couple of years old. Consider the Seversky P-35. It was a big deal in 1937 when the Air Corps got their first shipment, but by 1940 the plane had faded from the scene (except in Sweden, which ordered P-35s as late as 1940). Similarly the DC-4E airliner, which makes an appearance in issue #2, was a prototype aircraft that flew in 1938-1939. It proved impractical and wasn't developed further. By 1944 it was largely forgotten. The DeHavilland DH89 in the same issue lasted a long time--some are still flying--but its big news years were 1934-1938.
Another point worth considering is that between 1940 and 1944, when these books were published, a whole generation of new aircraft had appeared. The fighters and bombers that fought WWII fired the public imagination for years, but there's nary a hint of them in these stories.
As for cars, by 1940 almost all American car makers had switched to integrated front fenders with built-in headlamps. The previous formula, with separate fenders and headlamps mounted to the radiator housing on stalks, was still the dominant design in 1938. The big changeover began with the 1939 models. Most of del Villar's cars follow the 1938-and-earlier designs.
Any one of these points by itself doesn't prove much, but taken together they build a strong case that the Dani/Daniel the Aviator stories were produced sometime during the period 1937-1939. Yes, it's speculation. But it's not impossible.
