Can't answer that.. I have started at 1mg (for ~8yrs), quit for a few months (2) and started at 1mg again (~5yrs).. Quit again, for 4 months. And started again at 1mg (1 month now).
There's no difference between branded versus generic Finasteride, both are the exact same treatment. I've used both branded and generic Dutasteride and there's been no difference. Both are effective for your hair.