BG is affected by stress, diet, good health/ bad health

BG is affected by so much (stress, diet, good health/bad health) that it is my personal opinion, this is what changes our BG. But who am I to say -- right? At first blush, it seems unlikely. However, Metformin is produced in huge quantities, presumably at different facilities (I am not sure about the number of facilities, but there are different generic brands). Did anything else change like using a different batch of test strips? Did you change, stop, or start any other medication on a about the same time table?

I have had something happen that makes me feel there is a difference in the Metformin I am taking or maybe it is a "fresher" batch for lack of a better term.
I was DX'd in Feb of this year and have been working on getting my numbers in an optimal range. After about 3 weeks I did ok for a week or two then my numbers were higher (130-190 range for the most part). Last week I got a new bottle of metformin and my numbers have been in a much better range (109-121) pretty much immediately. It has been consistently this way since I have had this bottle. I haven't done anything different, my life is still the same, no stress, no illness, the only thing that really changed was the new bottle. Is it possible to get an old or bad batch that lowers your numbers but isn't quite optimal and then get a better batch an it works great again? What can I do to make sure that I keep getting the best?