[delusional]

> But in general, identifiers have little currency outside the system that generated them

That's clearly wrong, because if it were true we wouldn't be able to identify anything. Identifiers are only useful in so far as some external party assigns a meaning to the identifier. Two systems MUST pick a common idwntifier to discuss a person. They MUST pick an identifier to discuss a technical field. They MUST even pick an identifier to discuss a technical protocol.

Identifiers are everywhere. They'll usually be translated into something internal at the edge of a system, but I bet the PNR is too.

[PaulDavisThe1st]

Most identifiers are for use within a system, and are not intended to be GUIDs, semantically. My name is Paul Davis, which functions well enough as an identifier within my lived community, but is pretty useless as "real" identifier for me, which is why other entities I interact with want my birthday, or social security number, or passport or ...

One can cheat on this for airline systems by taking the position that "the system" is the aggregation of all the different systems, not any one of them.