On this list of film holder specifications I found one film holder that had a major deviation in one dimension from all the others and it makes the design completely different. I would have considered it a mistake but I happen to have a film holder in that size and the dimensions fit the chart even though I know for a fact that the other film holders I've seen in that size aren't like the design on the chart and my film holder. Can you find the that one size and the dimension that would make it unlike the others?
I realize that this question is for a very narrow group and perhaps someone with a historical background or knowledge of film holders.
You lose nearly an inch on the "exposure width" dimension with the 11x14 holder, whereas all the others are much less, around 0.2" or so. This makes the actual exposed area about 10x14. Is that what you're looking for?
I'm not nearly old enough to know the why behind this.
There seem to be several discrepencies between this chart and my copy of the 1951 ASA standards for holders up to 8x10. I don't have time at the moment to go into detail. Maybe in a few days . . . .