Hey there Matt -
A recall seeing few photos of early (likely Waterford-built) with a round chainstay bridge only, but most of the ones I saw had the plate. I know mine does (a Toyo-built).
I've got a few of those early AHH's photo'd during visits to the RBWHQ&L -
they all seem to have them.
IIRC, the serial numbers have some designators. But, if it has Waterford-branded dropouts, I think that's a solid indicator. They were a bit more rare. The colors were lighter on some of the Waterford ones as well.
Jim