The 1E3 and 1E4 printings are the most common. Here are the others.
1E2, reasonably uncommon but not as rare as the 50c1E2-SO.
NGR, reasonably uncommon but not as rare as the 50cNGR-SO. Here are two shades.
NOP, just as rare as the 50cNOP-SO.
Here is the watermark. This stamp is a 1L2. There is a second 1L printing with a very light pink color that is rare. I did not find any in the large sample I am using here that I recently acquired.