The achievement is triggered by the process of receiving it via looting or purchasing the helm, not simply by owning it.
As noted in our Support Article, a Game Master is unable to assist in this situation.
Not only, but the Support Article was recently updated referring to Wrath of the Lich King and previously obtained Hallowed Helms and Sinister Squashlings.
Wrath of the Lich King Classic:
If you obtained the Hallowed Helm or Sinister Squashling in Burning Crusade Classic, this will not be counted towards the Achievement criteria in Wrath of the Lich King Classic, to complete the Achievement criteria you will need to obtain the Hallowed Helm or Sinister Squashling again.
No, overall there are very few Wrath bugs impacting the queues.
Not simply by having MVP status no, but MVPs are generally granted that status because they have proven themselves to be knowledgeable. In this case, Perl understands how achievements tend to work.
There are always exceptions to the rule, Brickbat, but those exceptions have rules. If we have specific policies on a subject, as we do with this one noted by the presence of a Support Article that covers it, then how to handle it is already outlined and there generally isn’t any deviation from that.