Pretty much every major protocol and API has tried to do this. MIME has its fixed header field. XMPP has 'version="1.0"' dutifully exchanged between every peer, every time. HTTP was standardized at 1.1 only to distinguish it from the (rather borked) 1.0. Even IMAP went through a series of versioned revisions (though later versions are themselves actually capabilities), and Mark was one of the first to identify this as a problem.
If you're only seeing this in hindsight, you're in really good company.
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