I think that it's better and safe to follow the instructions of your own brand cos the ingredients & nutrients formulae for #1 and #2 are set for bb at different stages. e.g. I guess for #2, there may be more protein/starch to suit larger bbs with more growing/energy demand. for some, #1 is for bb up to 6 months, for the others like Meiji, its for bb up to 9 months.
So I will change to Meiji #2 when bb reaches 9 months.