Your asking the right questions.
The tough part is getting the legally binding answers.
Do you have any paperwork that shows it as a "NEW" car sale ?
Ask the dealership if "they" will honor or BMW will honor the warranty for the FULL 4 years as sold ? if the answer is them then get it in writing from GM. If the answer is BMW ask them when you can call BMW to verify the change to 4 years was made in their system ?
exhaust all options with the dealer first, then call bmw and backup your claim with them.
Olds Starfire > Chevy Malibu > Isuzu I-mark RS & Honda Magna 500 > Grand Am GT & YSR50 > Nissan Maxima & Ninja 750 > X-Wife > Hyundai Excel > Honda Prelude > Honda Accord > Honda Prelude & Ninja 250> Infiniti G35 > E90 335i > Hyundai Genesis Rspec, Hyunadai Sonata > Kia Sorento > Honda CRV-EX