A year would make sense since Henry is now 11 instead of 10 like he was in season 1. I agree with the theory that the birthday scene in Lacey is going to be someone’s dream.
They might not show Emma’s birthday every season especially if there is a lot going on like there currently is in season 2. However, perhap’s they’ll show Emma’s birthday next season and it’ll be a big family affair.
What if they leave showing Emma’s birthday until the series finale. Then they can bookend it with the beginning of the series. So in the Pilot, Emma is shown celebrating her birthday alone then in the series finale, Emma is shown celebrating her birthday with her family.