> The business concept of the "real conceptual primary key" can change, perhaps dramatically, over time, as the business model changes. A real prikey never changes.

This confuses two different concepts:

If the conceptual model changes, then, yes, the candidate keys (including primary keys) of entities may change between the old model and the new model. This can be a pragmatic difficulty in migrating between different conceptual models, but that's a problem inherent in different conceptual models.

The value of a well-chosen primary key of an entity within any given model should not change, as the primary key should always be a value which identifies the entity such that a different primary key means a different identity.