Flew out on an E190 that up until about 4-8 hours prior to departure showed STRETCH in 1x2 configuration; actual aircraft was 2x2 with five rows of STRETCH.

After boarding was underway, a family started walking up the aisle, against traffic, repeatedly saying "There's no row 11!" They probably did OLCI before the aircraft was swapped, and nobody caught the problem till the passengers boarded and realized they had no seats. All worked out well, as the family got moved to some unoccupied STRETCH seats.

At this time of year, when load factors are high, it was lucky that there were seats available to move them to.