Sorry I am new to tritium dial models. So you saying tritium watches from 1990 usually aged well? U means just that particular year alone??
Btw I’m still very upset I saw the ad u posted for the 1680 full set too late.
My observation on patina on tritium over the years. Watches that have been kept away from daylight usually have deeper patina than watches that were worn daily and exposed to light. I've had two 1665s (a DRSD and a great white), a 1680, 16750 and two 16800s that had snow white tritium. All where sourced from owners that wore those watches daily. Moisture will also give a more brown rather than yellowish patina to tritium.
That certainly is the general theory. However, patina is a great watch mystery to me. My patinaless 16700 has mostly sat in a drawer for a decade and a half, and before that was mostly worn indoors with little UV exposure.