What other differences is there for label color (white/blue/others?) for spacesavers other than production dates?
Personally, the single component that might seem to make the most difference is the extra-heavy steel back plate. For standard Ms, the first plate weight reduction happened about 1987-88 at different times at different plants.
I have only had one SSK, a 1991 beige label, but I think that they were made at least as far back as 1988. Whether any of them had the heavy plates, I don't know.
You used to be able to get 1390120s cheap, if I could get one now I might cut the plate for my 1991. That mod, along with a white latex blanket from Unicomp (an easy scissors cut compared to the hacksaw nightmare) would be everything I wanted.