Vermonter here (born there, don’t have “seven in the ground”, and currently in New Zealand, so “real” Vermonters would take issue with me).
I have no frickin’ idea. However, my I will postulate that they are located where windows are needed, but a standard window size wouldn’t fit. Rather than a custom window having to be made, which would go against the legendary thriftiness that New Englanders used to be famous for, an off-the-shelf window was purchased and simply framed in parallel to the roofing beams.
Most of the windows of this type that I have seen are on walls between two sections of the house, where one roof was maybe three feet lower than the other. I would imagine that these windows usually illuminated stairwells.
Someone once told me that they were to make it easier to get bodies out of a second floor, but I can’t see as taking a body out a window and down off a roof is any easier than just taking down a flight of stairs. Duh.
Googling for this info is futile. Another option would be to send an email to The Shelburne Museum (website at their name plus .org). The SM is reknowned for their collection of American folk art and old buildings (many dis-assembled and relocated to museum grounds). If you’re ever in Vermont again, don’t miss it (though it is closed in the winter).
Hope you had fun skiing. Snow is beautiful but I don’t miss it much. The weather here is just about ideal for my tastes.