Asked this today on RootsChat, also where I'm newbie, and awaiting moderation.
From the quality of responses in here, I'm hopeful of getting an answer to this

When a "certificate" comes back from GRO, there is a cover sheet with (GRO) Reference that is also printed (as Application Number) near the top of the certified copy itself. Never noticed that before, but handy - and perhaps useful as a personal file reference? To record in my citation details too...
What I have noticed before, and always wondered about, was the rather "official"-looking reference number on the copy's bottom left (an example is shown in this topic title for a marriage). One birth example starts "BXCJ".
That has to be interesting, whether useful or not. Any insider info in here, please?
Thanks,
Paul