New addition U serial Sub with "Swiss Dial" Tritium??

[Daso]

Hello All, I've had the urge to add a Sub or SD as my second Rolex and found a great companion to my Daytona 16520. Although I've read a series of posts still have to ask the same question. I have a T series Daytona and now added this nice U series Sub 16610 with the "Swiss" only dial. This watch with a U 400 serial dates to 1997. That being said if I UV my Daytona you get no lasting (Nada, Nothing Zilch) lume, but when I UV the Sub (see photo attached) it glows bright for a solid few minutes and fades within about 20 minutes. The watch itself is a really nice unpolished, honest piece and the dial is original. Are all pre 2000 Subs with the Swiss only dials Tritium or was luminova already being used as early as 97? My other vintage tritium dials (although mostly 30-50 years old) hold varying amounts of lume for much shorter periods of time. One final point is that my UV reflects blue on the Sub and green on my other tritium pieces. Just really curious as to the lume material of my Sub (I prefer tritium, but either is fine in this case). Regardless and although I am a chronograph nut, loving the Sub (or same if it was a sea dweller and deal was great) Thanks