I haven't seen one of those three-place receptacles for almost two years, now! BTW, triple switches were also made.
The wider, or 'polarised' blade was first introduced in the '30's, I believe, but other affairs kep it from becoming universal until the early '50's. Even then, many appliances had their shells grounded to the neutral...something that didn't end until the early '60's, with the general acceptance of three-prong receptacles.
What did the code say about non-NEMA patterns? Nothing- there were no NEMA standard patterns until the early '70's, I believe. Up to then, it was common for plugs to have two widely different ratings, and be used on teo completely different systems.
Non-NEMA patterns are still in use. The RV industry uses a non-NEMA pattern for the power pedestals found in RV parks. The 3-prong range and stove receptacles are likewise non-NEMA plugs. And- surprising no one here- California has seen fir to design their own.
