And crucially, I learned during this mess, the 737-900 was not offered in the ultra-high density configuration and thus had a continuous fuselage with no option for an exit door between the wings and the rear door. Therefore it does not have a door plug. The -900ER and -9 have the same fuselage design, with the option to be delivered either with a door plug and limited to somewhat fewer passengers (the option chosen by all US operators of the -900ER and the -9; a normal domestic configuration with a first class cabin doesn’t push the capacity limit without the mid-cabin exit door) or with an exit door (chosen by the likes of Ryanair for an ultra-dense configuration).