I made sure to shop around and even asked my neighbors who had the same houseplan about the electrical work they had to get done in the past. The previous owners had neglected to replace some components that had been recalled decades ago, so that obligation ultimately fell to me.

I did manage to get a few things grandfathered in, like being able to keep a three pronged outlet for the dryer. But ultimately I made peace with the fact that the house's electrical system was in a neglected state and the fixes simply had to be made.

Many things are grandfathered. But not all.

Sometimes it'll be at home owners discretion. For example, I have a Pushmatic panel. The thing sucks. So even if it's grandfathered when I have other work done, I'm still getting rid of it ASAP.

Most things are grandfathered in. In my experience, sometimes even if it's not something your inspector should technically let pass, they will if it's existing construction and things were made no worse than before.

I think there's some of this in there too. Out-of-code is grandfathered in unless you're touching that part of the system in most places.

And even if you're touching that part of the system, you can usually replace like-for-like without bringing it all up to current code, even if the current condition is non-compliant, you can generally put it back to the same level of non-compliance, even if it's with entirely new parts. (I'm not arguing that that's a good idea to elect as a property owner, but rather that NEC does not require "you touch it, you have to fully modernize it". This will likely invite an argument with the AHJ's inspector, if the work is subject to inspection.)