Mick,
According to the F3 manufacturing date by serial number page on Nikonlinks.com, your 1637xxx body was likely made in November '83. There is one marked 1640xxx that was sold at the end of January 1984. The other body, likely was made in July '85, as the 75 digits of the code signify, due to the fact that there's a 174xxxx body that was sold in March '86, and a 170xxxx body that was sold sometime in 1984.
The "O" is actually the letter "O", not the number "0". "N" is November, and "D" is December.
So, how Nikon did it was this way:
1 = January
2 = February
3 = March
4 = April
5 = May
6 = June
7 = July
8 = August
9 = September
O = October
N = November
D = December.
I guess it was easier to do it this way, than to change the four digit code to a five digit code and go 10, 11, 12.
Anyway, interesting tidbit about your first F3HP and the rep recognizing it as being a German market body. Must've been in the serial number block that was shipped to Germany in late '83, early '84. So far, I've owned three bodies in the 16xxxxx serial number block. Two near the end, and one near the beginning. Also have owned two in the 17xxxxx block, as well as three earlier bodies, one in the 15xxxxx block, one in the 14xxxxx block, and one in the 125xxxx block. Plus the current P body and an earlier P, that was my first F3. That body was owned by the person who helped Nikon design the F3P, then sold to someone in Hong Kong, before it made its way to New Zealand. Afterward, it went somewhere else, and finally landed in the Seattle, Washington area of the United States. My current F3P came from someone in the UK. Not sure if he was the original owner or not.
-J
P.S. here's the Nikonlinks page...
Dead Link Removed