We have started given my son A+ no.3 this week. We mix it with no. 2 step by step, say in day 1, we mixed 90% no. 1 with 10% no.3 and in day 2, we mixed 80% no.1 with 20% no.3....so far is okay because with such graudual changes, he may not notice it.
My baby has changed to drink No.3 since he was 1 year old. He loves it very much without any resistance. He can drink 8oz or more. I just wanna make a point. My doctor says a baby can drink No.1 up to 1 year old. If your baby doesn't like No.3. You may change back to No.2. I don't think it will affect their health because milk isn't their only food. Think about it.
My son had been drinking no. 1 till 1 year old and we skipped no.2 and went directly to no.3.
You may consider drinking no. 2 till 2 years old.
Regarding the method that I am using, i.e. mixing no.3 with no. 1 step by step, I didn't consult the doctor or nurse but I have asked my friend who is working at the milk powder company. So far, the health of my son is quite okay and we have been mixing this for 1 weeks already.