When Did The Term "second-party Developer" Stop Being Used To Refer To The User?

I always believed that when it came to software for a platform the parties were referred to as such:

First-party: The owner/creator of the platform

Second-party: The user of the platform

Third-party: A developer who is not the first-party.

Now second-party seems to be used to refer to a developer owned/contracted by the owner/creator of the platform. When did this change in terminology come about and do we solely refer to "user created software" as such?

I think the notion goes back to commercial arrangements. The first and second parties are in a direct producer-purchaser relationship. The third-party parties are those other than the first party that the second party is dealing with. (Note that grammatical person doesn't quite fit, but it is a cute idea. It works better if the first party is the customer and the second-party is the primary supplier.)

In this context, it is perhaps overloading too much on the term to say second-party developer. The second-party might be an IT organization and have to do many activities to install and use the products and services of the first-party. It might farm out a lot of that to third parties, too.

Perhaps the key thing is that the third party is generally not part of the (business) relationship between the first and second parties.