That's about what I thought. This is exactly what is confirmed by the materials that I found on the web.
Maybe the availability of protection also depends on other factors. I read that the winters in 1970 were very cold and the bay froze. It is possible that there were such cold winters in other years. Now most of the skipjacks are not equipped with protection. Of course, many are used for other purposes and are pleasure craft. But for example Catherine (built in 1901) is an oyster boat. And there is no protection on it. Is the reason for this an increase in water temperature?
Or is it the economic situation in the region or the country? In difficult periods (the Great Depression, World War 2) is not up to oysters, oyster fishing is not conducted, therefore protection is not needed? What was the price of steel sheets in those years? If business is not going on, then there is no money for the maintenance of the vessel?
I made a list after studying the photos. Some of the photos of skipjacks with ice protection date back to after 1945 (for example, Fulton T. Mister, E.C. Collier). But some (Silver Spray, Mythle) have protection in 1910-1945.
There are such as Geneva May (1939 there is no protection, 1950 - sheets). The presence or absence of protection from ice is unstable. Both options are equally true. I didn't find any photos of Willie L. Bennett.