The question a version has to answer
A customer got an answer on a Tuesday in March and somebody is now unhappy about it. The question is not "what does the agent say today". It is "what was serving on that Tuesday, and can I put it back and see for myself".
Most of the stack answers a narrower question than that. Model registries version the model. Prompt tools version the prompt. A knowledge base product will pin the association to a knowledge base rather than its contents — re-sync the documents and every earlier version quietly changes meaning while keeping its number, which is worse than having no version at all, because it looks like an answer.
What is inside the number
A release here pins four things together: the knowledge base contents, the policy that governs what may be said, the evaluation suite that had to pass, and the model. It records who published it. The record reads: this agent, these documents, this policy, this model, passed these standards, signed off by this person.
That is a sentence a compliance owner can sign, which is the actual product. Everything else on this site is machinery in service of being able to produce that sentence truthfully.
Why a changelog is not the same thing
A changelog is a description of a change, written by hand, at the moment somebody remembered to write it. It is evidence of intent, not of state. The gap between them is where every awkward conversation happens — the change that was made and not written down, or written down and not made.
Publishing a policy version from the console serves it. There is no separate deploy, and no window in which the document and the running system disagree, because they are the same act.