Seamaster 2531.80 serial # production year vs warranty card date

The serial number charts on the internet are approximations only, they’re +/- a couple of years and are notoriously inaccurate for moderns watch’s like the sm300

How can this be the case? Because the information you are looking at is junk. You can't date a post 1990 Omega using simple online tables, it more complicated and requires interpolation from known data. Read up on the subject here. A 60m serial is right for an auto example from around 1995-2001. If you offer more granularity, ie more digits we can comment further.

One quick way to say if the watch is pre or post 1997 by the way is to look at the lume. Does it have tritium or Superluminova lume? SL was used after the 1997 change, tritium before, they look very different. Assuming the dial is original, that is a quick way to roughly date a 1990s SMP, assuming the fitted parts are original.