maxrpm,
CRJ has a new reinforced doors because the whole fleet had to go through with the retrofit.
I was working on a certification report for that door so I can confirm that one personally.
FAA, JAA and other CAAs required these doors on all passenger a/c.
I do not know where was the bottom limit, on weight probably (plus type of operations).
Bottom line is that CRJ 100, 200, 700, 705 and 900 all have reinforced flight deck doors.
Cheers