coulld some T206 sheets have been cut down and then had the backs printed?

[steve B]

It's possible, but I think unlikely. Most of the evidence we have points away from it being done that way.

If that was what was done there wouldn't be a need for the marginal cutting lines on the back but not on the front. And I can't recall seeing a T206 with a cutting guideline on the front at all.

Most of the groupings point away from that as well. aside from the overprints150 has very few no-prints and most of them are withdrawn cards.

It's possible that it was done the other way around, fronts printed on a large sheet that then received multiple backs possibly with some space between panels.
But there's no proof of that either, so it's purely a wild guess.

When I have these sorts of ideas, I try to figure out what the sheet would require technically for it to be workable on the shop floor. Multiple backs from the same sheet, or cutting a sheet down to print different backs would be more chaos than you'd usually want for a print job. So you'd need markers on the sheet fronts indicating what backs they were intended to have similar to the factory numbers in the margins.

Of course, that doesn't mean things weren't done oddly to push out as many cards as possible. I know of another very high volume print job that produced occasional waste "scrap" some of it because they were producing two different but nearly identical products but the entire sheet wasn't scrap, just portions. And when those portions added up they sometimes got converted to a different version of the same product.
http://siegelauctions.com/enc/pdf/1923Rotary.pdf

Steve B