I might be late to this conversation however had found the following when writing an article for my societies publication years ago about bay window boxcar cabooses:
E M Helgeson, General Chairman of the Order of Railway Conductors wrote to NP General Manager W W Judson asking that any future cabooses retain the cupola feature.
And here it is:
"In addition, another concern was when stockmen (drovers) rode in the caboose accompanying their stock, they insisted on keeping the lamps lit. Often reading as they rode, the light affected the crew's ability to see out the windows; Cupolas being apart from the main body of the caboose were always dark."
Letter, July 15, 1942 Superintendent Flynn to W W Judson, Presidents Subject File 24,
Minnesota Historical Society
Jim Dick - Roseville, MN
PS - the reading material of the drovers? Zane Grey novels another letter lists.