Greatkingrat - this is indeed the case - so if anyone fancies going to and from Amersham all day on that Wednesday, sat on an A-Stock... now is your chance! I'd imagine quite a few other people will also be riding it that day too!
Snudge27 - Possibly jammy, possibly, not, because as of this afternoon, there were still about 20 or so seats left, in carriages 4 and 5!