I had a ton of enfamile formula left over when my doctor okayed the switch to similac, and i just let him finish the enfamile before i switched him. it won't hurt to let them finish the enfagrow before switching, and if WIC or wherever you get your checks from finds out that you're trying to switch you can get in trouble. I'd just finish the formula checks you have and then switch.
Re: H enfagrow checks w similac checks