I just looked at my B12 box. Expiration says September 27, 2021. I'm doing 3x/week so that's going to put me over the expiry date and into October. Should I ignore the September 27th expiry date?

Yes, I wouldn’t worry too much about the expiry date. Many pharmacies are required to put an expiry date on their prescriptions, even if it doesn’t actually expire on that date.

I know it doesn’t make any sense but that’s just the way it is. The printed expiry dates are not accurate at all. 

I remember a pharmacist telling me that once. They’re absolutely required to add an expiry date on certain products. But it’s just an educated guess. They often don’t know when it will actually expire. So they just put something on it. 

So as long as you keep the methylcobalamin in the refrigerator and cover it with aluminum foil, it won’t go completely bad for a while. It will be fine and continue working after September 27th.