Proof appears to be in the pudding here. They absolutely overbook, all airlines do. Dated a few attendants over the years and they’ve all echoed similar experiences with folks being double booked especially so during this time of year. I’ve been bumped on a SW flight, got the extra travel voucher so it worked out. They absolutely do overbook.
If you read the linked faq, there's a difference betwen overbooking and overselling. If Southwest sells all the seats for a segment, but they end up flying the segment with a different plane than scheduled, there may be less seats than scheduled passengers. That's more likely to happen furong the holidays when flights are very full and weather delays are common and there's more equipment changes.
The difference is intent. Overbooking intentionally creates conflict likely to result in a ticketed passenger unable to board. Overselling also results in a ticketed passenger unable to board, but was not intentional; at least not directly intentional. You could argue flying planes with different capabilities offers the possibility to have a lesser plane subsituted and that's an intentional choice, but...
Another way to think of it is what could an airline have reasonably done to avoid the situation? If it's overbooking, the reasonable thing is to not overbook. If it's overselling, they could choose not to fully book their scheduled equipment, but is that reasonable? They can't choose to have 100% reliable planes and crews and weather and ground operations. Stuff happens, and it's certainly reasonable to be upset when it does, but understanding why it happened can be helpful, so making a distinction between overbooking and overselling makes sense to me.
The airline sold you something that they can't deliver because they refuse to keep extra planes around. They refuse to keep extra planes around because that would eat into profits, and would mean their execs wouldn't be able to buy their third gold-plated yachts.
No, they're all 737s, but there's a lot of variation within that.
Seatguru says [1] southwest flies three variants, 737-700 with 143 seats and 737-800 and 737-Max 8 both with 175 seats.
If a -700 gets substituted in, that's a lot of missing seats. I've also flown on planes where one seat is out of service for whatever reason and usually has a plastic cover on it.
