So, what do you think of my previous suggestion for adding Version-Number in returned headers of Metadata request? (HEAD /structured-data/{Handle-Id})
This field would be present for any tag (500, 501 and > 15000) in addition to existing Is-Owner field.
For tag 501, I also wonder if the number of versions is always equal to version number plus one. If this is true, then my suggestion would have the added benefit to allow removal of Get Versions request. (HEAD /structured-data/versions/{Handle-Id})
This is not useful because Is-Owner is already returned by Metadata request, that would make 2 redundant ways to get this information.
Adding Version-Number to Metadata request seems more useful because it provides a new information currently not available and it may allow removal of another request.