Flush Edison-base wall receptacles such as this one were probably never all that common. Most residences would not have had wall receptacles at all before the late'20s--if you needed to plug something in, you used a "cap and base". It would have been a fancy house indeed that had wall receptacles before T-slots became common.
I'm not sure what year these were banned definitively, but they were increasingly discouraged throughout the '30s and seem to have disappeared entirely by the '40s. My '36 GE Supply catalog does not list them. T-slots seem to have been the standard in the '30s, as there were probably at one time almost as many tandem plugs as parallel.
The fourth edition of the American Electrician's handbook (1936) shows an illustration of a parallel-blade (now NEMA 1-15) plug cap and base:
Attachment plugs were formerly made in a variety of designs. In general, a plug of each different design required a correspondingly-designed receptacle to engage it. Almost endless confusion resulted. But now, largely through the efforts of Electrical Merchandising, the Standard plug cap with parallel blades (Fig. 9E) is almost universally employed.
--SNIP--
In general, only Edison-screw-plug receptacles (Fig. 9G) or standard parallel-blade plug receptacles (Fig. 9H), should be used in ordinary interior wiring installations. This is recommended to insure that the standard attachment plugs, shown in Figs. 9E and 9F may be used in the receptacles.
