I owned a house on the edge of Richmond VA which was built in 1926 ...and by the time I came along, it needed a lot of rehabilitation. The walls-studs (which actually measured a FULL 2 inches by 4 inches) had been put in place with square nails. But the interior door-trim of every room's door had round-nails. All the baseboards had square-nails. So in 1926, houses in a state capital city were still being constructed using a MIX of lots of square and lots of round nails.
By the way, you may find this interesting:
The very old lady who lived nextdoor told me her husband and brother had built my 1926 house. She said they ordered ALL the materials (floor & wall lumber, nails, siding-borads, trim, pipes, tin roofing, etc etc) as a UNIT from the Sears & Roebuck Mail Order Catalog. It showed a picture of a completed house with one catalog item number ...order that item (the house) and you'd get all the materials needed to construct it, as a package-deal. So, clearly, Sears was supplying extremely large quantities of square-nails for home construction purposes in 1926.
Regards,
TheCannonballGuy [PCGeorge]