I too understand that the problems had initiated in the roof ADF window, but assumed they had gone through the same design and revision process as the cabin windows, ie originally spec'd for Redux then revised to redux + rivets, is that correct, or were were they just riveted without Redux?
Seeing as Caravelle and L1011 managed well enough with "cornered" windows suggests to me that de H wanted to put visible distance between early and later models so that everyone could see that "the problem had been fixed" even if many then and now do not fully understand the exact cause.
Whenever I hear people blaming the window shape alone as the cause I refer to Caravelle and L1011 windows to show that things are not always as simple as they seem!