One possible explanation for the difference in print ratios could be related to the initial crude design. It has been documented many times that Cy Berger created this set over his kitchen table, and some half sheets still in existence support this contention. Examples of sheets exist where the borders don't even match up...resulting in notoriously poor centering when the sheets were cut.
Taking this one step further - maybe some of their 3rd sheet mid-series production was never distributed due to poor centering. The only gray backs I seem to find are the ones that are off center 95/5!
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