Was it ever acceptable in the past to use 20A breakers with 14 AWG wire?
The short answer is NO. 20 amp fuses and breakers have been the rule for 12 awg and 15 amp for 14 awg. This goes well prior to your home being wired. Some one may have swapped them out over the years to prevent tripping at an increased fire risk. Because they used 12awg for the run. It also have been done by a contractor with good reputation and not caught because of the 12 in the panel. Not all states use the NEC today and back then there were more not using the NEC.