Globaliser.....
"Did the suitcases get stickered by security after being X-rayed? If so, they're then OK as checked baggage." - Yes, they did (rather fetching little green ones). Mine was carried on, my colleague's was checked in.
"Your briefcases, coats, etc. get screened as cabin baggage when you're airside after you leave the main shopping area, at the entrance to the pier where your aircraft's gate is." - Definitely NOT. As I said, there were no other checks after check-in. Perhaps what you're saying is that this should have been the case but on that particular evening, no. Because we were on a tight schedule between Sydney & London, with meetings in Bangkok in between, everything was rushed. It was only when we were chatting over dinner onboard that we both realised that there hadn't been any further checks.