What (if anything) are the standards for "generic" part numbers?

A very few components are actually standardized by JEDEC (think of the 7400 logic series, for example).

Most of the components you mention are simply results of historic multi-sourcing agreements: Large customers (esp. of the military kind) wouldn't buy an obscure part that they could only get from one party.

Also, don't underestimate the history of these companies: for example, TI having all the parts that are still available in stock under the brand name of National Semi happens because the former bought the latter, and some stocks simply have a half-life of roughly eternity. Mergers and spin-offs sometimes leave multiple parties with access to the same IP.

To answer about guarantees: Um, these usually don't exist. Good luck out there and read your datasheets!

I’m not intimate with all the details of lapsed patented designs and cross-licensed designs but I’m pretty sure the part numbers you mentioned have all expired their OEM copyrights and unless guaranteed by design ( not tested) these specs must be universal for each package. Construction and protection may vary.

These guaranteed specs are the details defined in the datasheets in tables with environmental and process limits, while the graphs for nominal are not guaranteed. They apply only to the manufacturer and the Design Engineer must ensure any alternate source in the “approved parts and suppliers list” aka AVL , —the new must meet your design requirements. You cannot always assume, even if most are the same.

The exception is if you know there is no critical difference in your requirements, you may specify any source, but pro’s take sub’s seriously.

Enforcement is only by specs, PO’s and the buyer’s financial clout.