Hey everyone

New dad here with concerns...my wife has gone through WiC and each appt they changed the brand of soy formula. First enfamil..then gerber goodstart now similac soy. I see each contains similar ingredients while variations in things like calcium and iron. The reason for concern is when my son was on enfimil..stool was turd like and a yellow light green color. On goodstart it would vary from turd to splatter but it was a heavy dark green almost looked Grey and now on similac soy it's a heavy green but always splatter no turd. Question is should my child be on one brand of soy formula or if WiC changes it per month it's fine?