As for people entering for the wrong continent, that's subjective and I don't think it can be easily enforced. Really, I could set my flag to pretty much any country I wanted to and you wouldn't really know the difference. (Well, unless I didn't speak the language!) That is hard to enforce.
Rating based tournaments, on the other hand, are enforced by the system. Since it's based on your highest rating for the last 30 days at the time you entered the tournament (not the time the tournament starts) you can easily have a higher or lower rating than the tournament is created for. If your rating fluctuates outside the rating band for that tournament, prior to it's start, it does not disqualify you since you'd already entered. Obviously, during a tournament someone's rating is likely to vary.
For the recent banded tournaments, it's entirely possible for someone to have joined two of them. If their rating was close to the cutoff point (and was close to their highest rating in the past 30 days), they could have joined the lower banded tournament, won one or more games, then joined the higher banded tournament.