Was there a period, ever, in the days of the big round dial where there were 4 stall-crashes in the space of 5 years (to scheduled passenger flights)?
Such question makes no sense from the statistical point of view. Air traffic in the old days was a tiny fraction of what it is today so you can't be looking at absolute numbers but on the other hand we know that the accident rate say in the 60-ties was 30-50 times higher than it is today (depending on aircraft type). For example 777's accident rate is almost 40 times lower than 707's. You get pretty good aircraft accident studies that go back to 1959, as for accident 'causes' there are almost 30 categories and stall isn't one of them, however they have LOC-I (Loss of Control in Flight). You would have to dig into archives to see how LOC-I rates vary over time however I suspect you could not prove in numbers that "stall" today is more common today than before - there are simply way too many technical factors and they are all interrelated so isolating cause to "round airspeed" versus "tape speed" would be simply impossible.