The E3 added the grooves on the safety bar, so that makes the determination. Appleby made his chart years ago and it has not been updated, hence BBS-1'S thread referenced above.
I think i've seen that thread a few months ago, but aside from the patents, I barely see any difference between the different E types. I can spot a pre/post war or 50s, 60s, 70s Tech from miles, but I find Schick E and G types very confusing. I need to find some high resolution pictures to see those small details and save those pictures in case I come across one in the wild.