Just to update.
I got out of there a few minutes ago. This is the first time I’ve ever gotten my extension done at CW before lunchtime.
i usually judge how busy they are by how many empty seats are in the waiting area. Today there was never a time when all the seat were full. About 10-15% empty chairs on average.
I did include a printout of the most recent TM47 receipt that I get via email, and they kept it.
As usual, there seems to be something very mysterious or interesting in my passport because they always spend a lot of time carefully inspecting the stamps from ten years ago, even calling over other immigration officiers to have a look. Wish I knew what it was.