well maybe a few pics of your could could reveal some better info for us hehe.
But yes if it has the white stickers with the Black ink tekst saying in capital Western Letters: "NOT FOR RESALE" it's a prototype allright
Anyway that is known in the most Prototype occasions.
And the 3dfx Voodoo5 5500 AGP x2 64MB Rev.A0 1400 is known as a prototype in the archives, Osckhar has that device
But if your Voodoo5 5500 AGP x2 is a Rev.A0 1400 it is deffintely a Prototype, because a Rev.A0 V5 5500 AGP isn't common at all, the production models of the 5500 AGP are all but Rev.A's
with the following Rev and PCB dates:
3dfx Voodoo5 5500 AGP x2 64MB Rev.A 1800
3dfx Voodoo5 5500 AGP x2 64MB Rev.A 1900
3dfx Voodoo5 5500 AGP x2 64MB Rev.A 2100
3dfx Voodoo5 5500 AGP x2 64MB Rev.A 2300
3dfx Voodoo5 5500 AGP x2 64MB Rev.A 2500