I reckon it's more likely to be 19 teens. The whole thing shows no protective earthing - the references to earth appear to be neutrals. In the 30s earthing was standard & 3 pin (earthed) plugs common. The few illustrations of 3 pin plugs in this are dual circuit, no earth. Even when earthing was just begining to be used I'd expect to see an apprentice include the concept at least somewhere.
It also shows widespread use of odd voltages & series bulb adaptors, eg 50v.
It also IIRC shows V & A meters at the fusebox, something that stretches back well before the 20s & 30s.
Bedrooms show ceiling lamp plus over bed light and/or plug-in socket, but I expect those would be luxuries seldom fitted at that time.