a few days won't make a difference. stage 1 is the best as there's no sucrose while the subsequent stages, the milk tends to get sweeter. If cost is not a concern I personally will continue with stage 1 even after past 6 months, but too bad stage 1 milk is the most expensive. as such i will keep to stage 2, but never beyond that. I'd rather let my child drink cow's milk than stage 3.
Im still feeding my 14 months old stage 1. He got constipated when we transitioned to the next stage so dont want headache, i just stick tk stage 1
personally, i'll go with stage 1. though its pricier, but there's a reason for the different stages. take note on the nutritional facts
I just moved onto stage 2 when the same happened to us
in my case, i did stage 1 past 6mo