I'm sorry, I don't get it. For session cookies, the client cannot do any validation of the cookie, so it's a completely different domain.
Also, unlike session cookies, SSLv2 never had a hard expiration date after which it could be unconditionally rejected.
However, I did just realize that for perfect security, there must be a service disruption on change of version. Otherwise you may be upgrading an attacker's forged v1 cookie to v2, if they submit a request before the v1 expiration.
Upgrading cookies is a bad idea. Revoking them and requiring reauthentication is better. See the talk I gave at Google on web crypto where I talk about exactly that situation.
Also, unlike session cookies, SSLv2 never had a hard expiration date after which it could be unconditionally rejected.
However, I did just realize that for perfect security, there must be a service disruption on change of version. Otherwise you may be upgrading an attacker's forged v1 cookie to v2, if they submit a request before the v1 expiration.