So, I guess there were 5 versions of the compact 50mm f1.8 Nikkor:
E (ugly), E (pretty), AISn (plastic), AISn (metal), AF (hmmm, three
versions of this: thin-focus-ring, rubber-ring, and "probable"-D) -
so, I guess that makes 7 versions total + the AI and AIS versions
of the larger, metal-barreled 50mm f1.8 - making 9 versions of
the Nikkor 50mm f1.8....!!! ;-)
Hope This Helps