I'd contend that it was "made" at all.
When I first looked at the relevant section of the policy manual, my takeaway was that they had a script that iteratively removed the leading and trailing optional fields, making use of the separators safe only if the fields were there so the script did not misfire.
They then took the runtime behavior of that existing script and called it the standard.
https://www.debian.org/doc/debian-policy/ch-controlfields.ht...
But in any case, this works.
Actually, I think I variable-width lookbehind might be handy here to check the hyphens, but I don't have Chrome 49, so I'll forgo it.