(Pardon me if this should be in the Ranma forum, but I felt that it should go here instead of there, since this concerns fan-fiction, not the series it's based on.)
I've come across a surprising amount of fan-fiction stories where, in the Tendo home, the bathroom is upstairs, and/or the living room furniture is Western (usually high tables with matching chairs, or a couch). Would that be considered enough to make the story an alternate universe, if the changes made to these common settings are never explained? I suppose it's not out of the question that the furniture is possible, since they do have beds in the girls' bedrooms, but what about the bathroom?
I'm well aware that this kind of issue can simply be swept under a rug, because it's not really important when you take into consideration a lot of other things about the series, where changes would be scrutinized with a lot more stringency. What about the technical side, though? How many unexplained changes can you make, before something becomes an alternate universe? Is it only when the changes are blatant or extreme enough? Or is it so sensitive that any work of fan-fiction could potentially be considered an alternate universe?
(Yeah, I'm bored. That's what I get for not having a life! *I shake my fist at the heavens!*)