New Vegas actually addresses the treaty thing with Mr House iirc. House wagers that while the NCR could push in and take the Mojave after eliminating the Legion, that they wouldn’t for two reasons. Vegas is popular in the NCR and a hostile takeover would be unpopular, and the NCR is afraid of loosing too many troops and also damaging the Strip, rendering the victory pointless.

The time change of the bombs dropping is a straight up inconsistent. We’re always told they were dropped in the morning but time zones are almost never accounted for.

I’m also not really sure what NCR water issues and Legions existence really means. Water is always going to be an issue and the Legion has a very good explanation and backstory that’s well thought out. Even if you’re referring to how the NCR hasn’t wiped them out yet, we get good explanations on that as well