Sea Dweller (questions on differences)

[RazorD]

Hello,
I am flirting with the idea of picking up a Sea Dweller 16600 and doing some initial research. My question is: are there any differences amongst the years produced (serial letters). If so, what are they and are there ones that tends to be more highly sought after or command a higher premium?

Thanks in advance for any information or direction you can provide!