To anyone still here in this thread, our May 15 Paris - London Eurostar went off without a hitch - except for the unseen - couldn't be anticipated, non ticket, no ID person who managed to somehow get on to our platform before boarding & delaying departure by an hour.
Those who had gone down to the platform - me - had to go back thru passport control & security.
Those who had not started down to the platform - she, 3 people behind me - ended up going back into the concourse waiting area. That group accounted for most of the passengers.
Uneventful, other than that.
And, yah, arriving at gare d nord two hours in advance is plenty too much time. 90 minutes, max, should cover it, under normal circumstances.
Thanks to all who provided info here & happy adventure s.
Terry