Each state of the country (and some cities) have different rules many times. And they will have adopted differing versions of the National Electrical Code - have their own “amendments”.
In my area you can just replace the main panel and bring everything to do with that (including grounding/bonding) up to code. But if you start remodeling the house wiring, then more older existing things will be required to be brought up to code. Like smoke detectors!
Anyway get it straight from the horse… Go ask your local electrical inspector!
A lot of jurisdictions have started to modify their codes this way.
The problem with the old version was that it often required a complete re-wire of the whole house, and that was so expensive that the homeowner dropped the whole project (or did it illegally, without a permit or licensed electrician). But the city wanted to see people investing in upgrading their homes, and electricians told them that a proper replacement of the main breaker box wouldn’t make the grandfathered old wiring any less safe.
So they modified codes to require only the part of the system being worked on to be up to code. (Often, they encourage upgrading other parts of the system, by allowing any other wiring changes done at the same time or within X weeks to be covered under the one permit, for one fee.)