Yes
Wino, hit the nail on the head!
Did a N. Atlantic crossing about 18 months ago. Planned at FL360. Took off from LHR several tons lighter due some freight not making it.
Asked by ATC about 1/2hr after takeoff if could take FL380 now and for the crossing. Checked MAX ALT and it was FL392 so no problem and the oceanic entry point was at least an hour away giving an even greater margin.
About three hours into the flight, in the vicinity of Iceland, I noticed that the thrust levers had been well forward for some time. I looked down from my newspaper
and saw MAX ALT FL368 on the scratchpad and the yellow lines almost meeting in the middle of the speedtape!
It was a rather interesting situation, sitting there with full chat for about 15mins - what made it even more novel was another aircraft 1000' lower, directly underneath. We held our breath for a bit but luckily it was flat calm at 380 and the air slowly cooled off over the next 1/2hr and that combined with the weight reduction brought us back inside the envelope.
At FL380 the TAT was +3, i.e. nearly ISA+30. TAS was well over 500Kts, which was nice, but I would have traded that for a little more margin...