Two more travel experiences
Flew Virgin Airlines from Orlando to London Heathrow and then back to Orlando from London at the end of January. No problems whatsoever. Never even asked to see the extension letter upon return to the USA.
Flew from Orlando to Santo Domingo, Dominican Republic and then back to Orlando at the beginning of March. Again, no problems. This time I was asked for my extension letter upon arrival back to Orlando, but they took one look at it and we were good to go.
In all, have been back and forth to Canada about 5 times, gone on a cruise to the Bahamas, a trip to London, and a trip to the Domician Republic on my extension letter and it has gone very smoothly each time. The biggest holdup was the cruise to the Bahamas because the Royal Caribbean employee needed a manager to sign off on it on their computer.