2B2 is where the bore is a true 82mm. If you look at the engine workshop manual you will see there are a selection of them for different manufactured tollerances. Some engines have a mix of pistons in (rare) and some engines are all not 82mm bore. The piston code will tell you either way.
If your car was built on a Friday then it could be anything Seriously though, 90% of engines are 2B2. If you have a 2Mx code on them or other code then your engine has already been overbored to the first oversize. It is always worth checking what they are so you don't end up with useless bits (be it rings or pistons)