Conductors Windows

Here is my silly question of the day.

Conductors windows as used on the Chili Line, were they used any where else.
Why were they not used everywhere.
How many cars were they applied too.
Why were they not removed when not assigned to the Chili Line.

What sparked my question was rereading an artical about the RMRC trip of 1947 pulled by RGS #20. In it there was a picture of the coaches, both with conductors windows, with the caption reading that the windows ment they were once used on the Chili Line.
I am thinking that they were used on other runs too, though I can not remember what one it was.

Please point me in the right direction.

Phil