Okay for the record I just wanted to say that Sherlock mentioning an underlaying threat of a birthday surprise party while talking John’s ear off (and this is an unintentional pun regarding the cardboard box, if you know, you know) about how absurdly in love with Christmas he is was not without a reason.
And if you ask me, when the boys come home after the cardboard box case, there will be a (threatening, if you ask Sherlock) surprise birthday party waiting organised by Mariana in cahoots with John. And John will rant before to Sherlock about something ridiculous to buy them some time, because they’ve finished the case too early and Mariana is not yet ready with the preparations. And there will be a cake, candles (maybe just a symbolical one, because Sherlock hasn’t told anybody how old is he, of course), and Archie with a birthday hat on.
And even though Sherlock might have not thought that his birthday was relevant, he will be smiling to himself after the party is over (and after John with Mariana had just given him the tightest of hugs, maybe even a quick kiss on a forehead, because this is our Sherlock).
You know, just for the record.