to the best of my knowledge they were made from 1947 thru 1955 1st series.
That sounds about right for GM trucks. Not sure about the late 47's having the 5 window option or not? But for sure from 48 - early 55
I have a 48 5 window.
Other makes have had 5 windows too, Dodge about the same time, and I have seen some new Kenworth trucks with corner windows.
Grigg