Can you enlighten us further? Nothing would surprise me, this could well be some bean counting plonker's idea of efficiency. I was told ages ago that certificates are only signed on Thursday in Queen St. Checking signature dates does seem to back this up, but I noticed it took more than a week for my recent renewal to progress from signature date to postmark date, and then it took 3 days to get 30 miles north of Aberdeen!
That said, I do agree that they are always helpful, polite and efficient compared to some of the horror stories related on here.