Let's say I passed my Class 3. And it has already been more than
a year since I've passed and my probation is over. I've got 24
points now right?
Then now I go for my Class 2B and I just passed and I'm on
probation for Class 2B. I'll only have 12 points for both Class 3
and 2B? Is this true? 
And btw, is it 12 or 13 points for drivers on
probation? 
Your 12/24 points applies to the specific class and not the
person per se. You have 24 points when you are behind the wheel of
a car but 12 points when you are riding a bike, also points not
cumulative or interchangeable hor - you don't have 36 points to
play with 
From my understanding 12 is the maximum number of demerits you
are allowed to chalk up, if you get 13 then its probably a
suspension/revoke depending on severity of traffic offence?