alt Hacker NewsNetwork protocol designers know better and by default embed protocol version number in message format spec.
I guess you can assign 3-4 bits for identifier version number as well.
And yes - for long living data dealing with compatibility issues is inevitable so you have to take that into account from the very beginning.
when I designed network protocols this is exactly what I did. I also did so in file formats had to create. But a database primary kea is not somewhere where that can be easily done.