Should an installation have been compliant when it was installed then it is compliant today even if we think it is unsafe. One example that keeps sticking its head out is GFCI protection. A house that has an outside receptacle that was built in the 60s is compliant with a regular duplex installed instead of a GFCI protected one. Would most think this needed to be changed to a GFCI device? Yes, but not required unless it was to be replaced due to any reason except the current code requirement.
The same is true with the other trades. A washing machine with a 1 ¼ inch drain that was installed 20 years ago is code compliant today although a horizontal run would require a larger pipe to meet todays standards.
What happens is someone new to the trades and not knowing the old codes would start making statements that this installation is not to code when they are in fact code compliant. I run into this in renovations all the time.
Bottom line is; if it was compliant when installed it is still compliant today even if we think it is unsafe.