People mean different things when they refer to sleeping through the night. My son's been doing that awhile - he usually sleeps 7-9 hours straight, eats, then sleeps another 2-4 hours for a total of 11 hours of overnight sleep. Usually. But he goes to bed at 7 so even if he sleeps 8 hours, he's still up at 3 a.m. to eat.
When did your baby drop the overnight feed and sleep 11-12 hrs straight overnight?