There are many different tournaments for bjj out there, and they all have slightly different rules/point systems.
For example, if you compete in NAGA, they allow dangerous leg locks in every division for no gi (including beginner division). They also award points for submission attempts, which is unique to their organization.
Also, depending on the tournaments, passing the guard varies in rewarding you 2 or 3 points.
Little things like that can definitely change the outcome of a match, and should be prepared for.
However, sometimes the rules don't quite explain whether or not obscure techniques are banned (and often times get updated after they assess the situation better).
Many years ago, one of my team mates was able to choke out his opponent using his belt in a tournament and won that way.
Yes you heard right: he used his belt like a hitman would choke out someone to kill them!
Subsequently afterwards, they changed the rules to ban this technique.
check it out: