Why is it so difficult to find Rosie's in circulation prior to 1965, but much easier to find Jefferson's and sometimes even quarters? Wheat pennies are also a much more common find in circ. than a Roosevelt. Is it because they are just so small and thin?
They are silver - therefore worth more than face value. I don't think you'll find that many 1964 and earlier quarters in circulation for the same reason.
Also, as I found out the hard was when I tried to spend a silver quarter last year, vending machines do not accept them. So, they stick out easily, and are weeded out one way or the other.
Most vending machines, coin counters, and Coinstar machines determine what value a coin is by its weight. The silver coins' weight is different enough from the clad coins that any machine will kick them out. It's why darkside (and greyside) coins are always unaccepted. For a US coin to go through 40+ years without finding its way into a vending machine is exceedingly rare, almost to the point of being statistically impossible. Even cents run into the weight problem. Until the zinc cents in 1982, cents weighed just over 3 grams. Now they weigh 2.5.
I remember in the late 70's as the Hunt Brothers were trying to corner the silver market. Silver goes to over $50 per ounce. As a paperboy, I turned in rolls of quarters and dimes (all common dates, primarily 1960 to 64 dates that I acculmuted from door to door collecting). After I cashed out these rolls that were virtually worth nothing from a collector's standpoint, I never had so much cash as a kid. My Dad told me, are you crazy?...the market is going up! 3 weeks later, the market comes crashing down. What happen to all of those silver dimes and quarters? They were smelted and gone for good...never to see circulation again. It was the last time I EVER made money in the commodity markets!