You made your API, you told people outside the company about it, you got it widely used. Are you free to deprecate it? Are you free to change it incompatibly?
You made your postcodes to better sort and deliver letters. That was your only purpose. You told everyone about them and kept telling them until absolutely every database with addresses included your postcodes, and people started using them for other purposes. Are you free to change them if some tweak would improve your ability to sort and deliver letters?
And it's happened before, will happen again, and is currently happening all the time.
In the U.S., we had postal zones in certain cities. A two digit code to specify where in a large city, the letter was to be delivered. The modern zip code wasn't widely implemented until 1967. And depending on how an area grows, it's possible for a postal zone to get subdivided changing the zip code for certain areas.
A better analogy is some sort of third-party API rating system. Consultancies put out big whitepapers about what a "storage service" is, and what the relative quality of things like Amazon/Google/Microsoft's offerings are. The change in definition of e.g.
Pluto might be analogous to that company originally having classified Amazon S3 as a "backup service" before deciding that it was really a new category of service that has now spawned many competitors.
The classification is designed to help us reason and talk about like things. We can all see how Amazon S3 and e.g. Dropbox are fundamentally different categories of service, and they need different names. We shouldn't be afraid of reclassifying things because people will have to change their models. The point of recategorization is that the old models are not as useful as the new models.
“Your only purpose”. As if such standards were set in place and there was no ongoing committee to deal with new cases and scenarios that arise as they inevitably do in any complex system.
But consider the same issue with different words.
You made your API, you told people outside the company about it, you got it widely used. Are you free to deprecate it? Are you free to change it incompatibly?
You made your postcodes to better sort and deliver letters. That was your only purpose. You told everyone about them and kept telling them until absolutely every database with addresses included your postcodes, and people started using them for other purposes. Are you free to change them if some tweak would improve your ability to sort and deliver letters?
FWIW I don't have an opinion on the matter.