MEL_Traveller,
Please do not take this as an attack because it may, unintentionally, sound that way.
You are saying "I am inclined to think cog is not an issue."
I am stating that it can be and is an issue in some circumstances. My statement is based upon 40+ years of aviation experience as a flying safety officer, accident investigator, pilot, chief pilot and a masters degree in aviation management. The comments are in reference to small through large size aircraft. The larger the aircraft the less issue one person can cause however all aircraft still operate near their limits on occasions. The extension of this is that it is unlikely to matter if everybody does not return to their original seat but it does matter that most return to their original seats. This is done via an announcement and by the crew keeping an eye on approximately where everyone is.