Why is Big-Lipped Alligator Moment a YMMV entry in the first place? A BLAM occurs "when something completely random happens"..."and has no bearing on the rest of the story". Maybe I'm dense, but i don't see how an example of this trope -and by extension a BLAM Episode- could be seen as subjective.
BLAM is a trope that seems to have both objective and subjective qualities. It's objective when the characters within the story seem to acknowledge that the "moment" was bizzare (like the tunnel scene from Willy Wonka And The Chocolate Factory) but so many editors want to stuff in other moments that they find to be bizzare, regardless of how truly weird it might be In-Universe.
Simply because it's next to impossible to keep the two seperate (Big-Lipped Alligator Moment is a meme far surpassing this wiki, making it popular and highly prone to decay), the trope was made YMMV just to try and curb the problem. It's really just a temporary fix and the trope should be objective, but like Complete Monster and Moral Event Horizon rampant decay has made it a subjective trope. See this page
for the trope repair discussion.
As for BLAM Episode, the criteria is almost the same as a regular BLAM, so just for consistency it probably should be made YMMV.
If the characters have to acknowledge it as bizarre, would the Trope Namer moment even count?
At first I didn't realize I needed all this stuff...
That sounds like a deconstruction of Big-Lipped Alligator Moment as I understand it.

As Big-Lipped Alligator Moment is subjective (and has the YMMV banner), shouldn't BLAM Episode be as well?