There are Spanish people who report Sex IN the City being changed to Sex AND the City

I'm not fluent in Spanish, but Google translate says Sex in the City would be translated to Sexo en Nueva York. Once again, there is very little difference (when spoken aloud) between "Sexo en Nueva York" and "Sexo y Nueva York." Even if you go with a more general translation like "Sexo en la ciudad", the difference between "en" and "y" hardly seems like a powerful example of alternate realities. I've got to go with Occam's razor on this one.

By definition, an alternate history is impossible to improve empirically - it simply doesn't exist any more.

By what definition? I think you're jumping to an unfounded conclusion here. If the alternate reality doesn't exist anymore, how can memories of it persist? Are memories not subject to the same laws? For me, the claim that it is impossible to prove one way or the other is a pretty paltry excuse. I believe we can apply a modicum of reason and rational scrutiny to these claims. We need not accept any and every discrepancy in memory as an alternate reality. And even if memory is the only thing that we have as evidence, a double blind study could be conducted to see if two people really do independently remember the exact same thing (with a reasonable amount of detail). But it would have to be something specific enough that couldn't be easily explained away.

I know your memories are real to you, but honestly, there are a ton of unsubstantiated claims out there, and I believe they undermine the legitimacy of this theory as a whole. If there's no room to look at purported Mandela Effects critically, we're really achieving nothing in this subreddit. Just a bunch of people talking about how they remember things differently.