Knowledge of codes varied widely back in the day as well as the enforcement of them.
Good example are 3 wire sub-panels which were never legal in the same structure but you can find countless apartments and condos built here and there up until the 90s with 3 wire feeds as well as 10-2 and 6-2 bare ground to the dryer and stove. (code requires the neutral to be insulated when using NM) Disposal or lighting tapped off the SABC, #14 to dinning room receptacles, GFCIs not installed despite being required at the time for that area, ect, ect.
Most of the homes are from the late 40s-50s. Some have tampering some don't, some have it just for the fixtures.