Well if you can't be convinced by facts, I can't help you.
Did you have a way to monitor the CO2 ppm? Was it administered ABOVE the plants (since CO2 is heavier than air)? Did you have an air-tight growrrom to allow the CO2 to build up to the proper levels? Did you stop CO2 augmentation during lights off? If the answer to any of those Q's was no, CO2 wasn't helping.
I've grown pot with a $1,000.00 CO2 set-up. It will gives you buds EARLIER than excellent ventilation, due to the fact that the plant grows faster IN VEG with extra CO2.
But when the buds are finished, they will be the same size.
BTW, the time you had small buds--were you providing flo-thro ventilation? I'm not talking about an open closet door, I'm talking about powered exhaust and intake, constant fresh air?
Ever seen the huge buds grown outside? About the size of your lower leg?
Grown outside, WITHOUT CO2 augmentation, just fresh air.