JG, the serial # does start with 550. When I bought the first pair around 2002, I also purchased a pair of 7X42 Zeiss Classics.
Both are excellent glasses, but for me the ergonomics of the Nikon pair was better and the view through a good pair of porro prism binoculars is more pleasing to my eyes. They have more stereoscopic effect because of the shape and I find them easier to peer through brush for animals. They are easy to use both with and without glasses. I get a full field of view either way. They are very sharp to my eyes and the view is exceptionally easy to acquire and for me there is never any eye-strain. Focus is crisp (the Zeiss felt sloppy in comparison.)
I often compared the two binoculars. I liked the Nikon SE best. I sold the Zeiss 7X42 binos a few years ago.
About the time Nikon was discontinuing the SE line, I bought the pair for my wife that are for sale. She simply does not use them.
What I don't like about the Nikon SE binoculars is the rubber fold down eye cups. Eventually the rubber split at the fold. (That pair was carried for 12 hours a day for three summers with the eye cups folded.) Also they are not fully weather-tight for snow and rain.
I still have my original pair with duct tape on the eye cups!
