Bill I do not know if 10/2 was "legit" only that it never failed inspection.
This would be around 82 to 86 Boston area.
I was a apprentice then and did what I was told.
Another short cut this company was good for, in sub panel applications we would rough in dryers with 10/3 and stoves with 6/3 AL SER this would pass on rough inspection.
Then when I was sent back to do finish he would have me use 3W outlets and cords, inspectors would never catch this.
When I asked why we bothered to run the right cable in the first place the answer was "because if we get caught we will not have to damage the building finish to fix it.
I work for a professional company now.