Originally Posted by
CJKatl
She is confusing the seat map with the seats available. There are seats that will never show as available on the seat map but are open, held for gate issue and included in the available seat count.
Exactly. I've had numerous occasions where I've booked a ticket late in the game, with the seatmap showing full, so I was not able to choose a seat at the time of booking. As CJKatl stated, seats are blocked out for crew, passengers with special needs, etc. Your MIL has a confirmed seat, she will just need to wait until she gets to the gate to learn where she will be sitting.