dating a 5512 sub

[dorianmaestro]

I have a fabulous sub that I am going to sell. I have tried to date it, but have found it's not that easy.
Model: Submariner 5512 with a 1.2 million serial number (no date). Problem is, I see that it is either 1964 or 1959, based on websites. I called my rolex dealer and he looked it up -- 1959 he said. I am still not sure, though, because I then saw that the word "superlative" was added later in the models. Can anyone help?

Thanks