Difference between 67-71 and the 72 doors

[purewhitemp5]

Everywhere I look it seems that the doors get listed as 67-71 and then 72 is listed separate. So whats the difference? Is it just the way the door panels are designed and mounted ?? For example whats the difference between a 68 door and a 72 door ?? I ask this because yesterday I was looking at my truck (dreaming is more like it) and thought to myself those ugly green door panels have to go and throw on some 68 metal panels. then I start to think , would they fit on the 72 doors? should have saved the old 68 door rust panels for reference (tossed into trash). If anybody knows thanks in advance.