DT Swiss Hugi / 540 tandem hub question

[disherwood]

DT Swiss Hugi & 540 tandem hubs
I have a rear hub of each type a hugi with disc/drum brake doughnut option and a 540 tandem with disk/drum brake doughnut option..... Both excellent lightly used condition

I'm interested to know how old these are..... What year did dt swiss / hugi begin adding the disk/doughnut option.?

Thanks for an help available..

David