From my experience: You should always update the referenced libraries (portal, doc-fcatory, cronjob, ...), it's just a technical debt if you don't do it.
If the difference is only a minor version (e.g. 12.0.12 -> 12.0.16) it usually works out if you continue using the old PMV, but side-effects can never be ruled out and therefore I'd just update the portal as well.
If the difference is a major version (like 12 -> 13) I'd always refrain from just converting the old PMV since it might not even compile in the new major version.
