JUST GOT TO THE END OF SPN S3E7

AND- AKSJKDSJKSAKSDJKAJK

DEAN IS “showing his little brother the ropes”

AKA- TEACHING SAM TO FIX HIS CAR!!

HIM BEING FULLY PREPARED TO DIE IN LESS THAN A YEAR, AND MAKING SURE HIS PRECIOUS BABY BROTHER KNOWS HOW TO TAKE CARE OF HIS PRECIOUS CAR IS JUST-

MY HEART CANNOT TAKE THIS!!!!!!

Because at this point, Sam doesn't know that the Trickster is an archangel, that he's already met an angel, or that angels can create pocket universes. And considering how everyone in that universe reacts (think the minimal concern by either the old man or anyone around by a hit-and-run) they're almost certainly creations of Gabriel. And with how Sam survives a whole 6 months without Dean - this is an angel pocket-verse, not Gabriel changing things. So we can assume Dean didn't actually go to Hell during those 6 months vs Dean going and having forgotten like he did all the Tuesdays/previous Wednesday. And so Dean didn't lie when he said he didn't recall much. He essentially was an actor exiting the stage of the play, in limbo until its time to return.

But Sam doesn't know that. He knows Dean is being made to forget things. He knows the Trickster can change reality (If he can throw someone in a wormhole, how hard is it to grab someone out of hell?). He knows the Trickster refers to Dean as doing the "hellfire rumba" right now. He knows if Dean dies early he should still go to hell.

But Dean doesn't know this. It's pretty clear that while Dean knows a little about the Mystery Spot incident, he doesn't have the full picture. So he probably doesn't know he died for 6 months in this pocket universe. (With how they struggle to express themselves normally and Dean's upcoming death being traumatic for them both, neither of them likely want to dig into this.) In Mystery Spot Dean has no visible tics he's lying (unlike later), this time he just looks confused.

So from Dean's perspective, when he lies about not remembering hell in 4x1, it isn't something he's trying to slide by Sam, say for continuity because he's told this lie before. Instead, this is a first-time reaction/lie you'd expect from Dean, whose trying to avoid talking about his feelings and trauma, and to hopefully to will the memories away.

Sam however is expecting Dean to say this. He thinks forgetting hell upon resurrection is normal, it happened to Dean before. Sure he wants to believe that Dean forgot, but having a precedent helps (he was pre-law after all). It's only when Uriel questions it does Sam start doubting the lie.

So it's crazy to me that Gabriel's experiment when he's trying to stop Sam letting Lucifer out, actually helped solidify Dean's lie to being even more effective, by drawing out the full reveal to Dean's hell experience until mid-season (for good or ill to how the season played out with Sam finding out later rather than sooner - and how that impacted Sam's actions in season 4 is a much more in-depth conversation).