Update on 737 Aft Door.

 The door - whether used or not - on certain 737 variants can be disabled. Watch this video for some interesting information on how that is done. 

Known as the MED, there are 2 types - active door and plug door. There are ways to tell the difference. Here is an image of the 2 different types. 

Here is an image of a Ryanair 737 Max8-200 with the MED active:

Here is an image of an Alaska Air 737-Max9 with the door inactive. 

I suggest going to Chris's website for all things technical with regard to the 737. I have spent hours lost in his information. http://www.b737.org.uk/ 

Check out this specific video. https://www.youtube.com/watch?v=maLBGFYl9_o