I recently bought a house which was made in 1965 and which still had the original Bryant outdoor main box and breaker, a subfeed to the original GE subpanel in the garage, and (with a few modern exceptions, which seemed to be added by the previous owner) the original GE breakers. Most of the wiring is 1960s-vintage fabric-covered, rubber-insulated 12/2 Romex which is still in reasonable shape. With the exception of some high-power circuits, like those feeding the electric oven, stove, a spa (which had been removed by the previous owner), electric dryer, and AC unit, all the circuits used 20A tandem breakers (see photo).
A neighbor having a similar house made at the same time by the same builder has a near-identical setup, with the same use of 20A tandem breakers for the branch circuits.
I've since had the exterior main breaker, subfeed to the subpanel, and subpanel replaced to support a solar installation. The new panel is a BR model by Eaton with more slots so tandem breakers don't need to be used. The electricians simply used new breakers of the same rating for each circuit (e.g. a 20A breaker in the old panel was replaced with a new non-tandem 20A dual-function AFCI/GFCI breaker in the new panel).
The new panel and solar installation was done by a licensed electrician and passed inspection. So far, so good.
I've been going around the house replacing old, worn-out switches and receptacles with new ones, checking for and replacing loose original crimp connections with wire nuts, etc., and noticed that several lighting circuits have 14/2 wiring but are still fed by a 20A breaker. It appears that those lighting circuits have 12/2 running from the subpanel to the first switch or fixture on that circuit, with 14/2 being used for the remainder of the circuit. From what I can tell, all the wiring is original 1960s vintage (i.e., the previous owner did not re-wire the circuits to use 14 AWG wire, it had always been that way).
Clearly, this does not meet modern code requirements and I've ordered replacement 15A dual-function AFCI/GFCI breakers to replace the 20A ones feeding circuits with 14 AWG wire to be safe.
Since the house was built by a reputable builder and presumably passed whatever permit/inspection requirements existed in the 1960s, that prompts me to ask: was it ever (specifically in the 1960s) acceptable or to-code to use 14 AWG wiring with 20A breakers for household branch/lighting circuits? Clearly this is not the case with the modern code (barring rare exceptions not typically found in a suburban home), but was it ever acceptable?