"Looking at the 737's crash history, there sure seem to be a lot of different subtypes for the 737."
I still do not know what those numbers stand for. I said that those were not MODEL numbers. This:
http://www.boeing.com/history/boeing/737.html web page shows almost all of the Boeing model numbers. I did notice that the -900 model was not listed, but it is the newest of the 737 group.