I was always impressed with the groundschool's instructors comment that the a/c could maintain (*maintain*!) a cabin altitude of 15,000' with the a/c at FL600 and 2 windows blown out (all 4 airgroups working).
NW1,
It's not impossible that your instructors were wrong....
This graph is from Chris Orlebar's book "The Concorde Story" (redrawn by me, because the original was too pale to scan properly).
It tells a very different story... after a window blowout you very quickly started an emergency descent, and in the worst case (only 3 airgroups working), the cabin altitude would still peak at about 40,000 ft for about 2 minutes.
I think we'll have to look at our flying manuals to setlle the question!
CJ