Excellent input from the previous posts. It is indeed true for older aircraft types, that continued to soldier on using the "grandfather clause", a nominal reduction in V1 was often given to provide a Vstop, but followed by a large grey area between the lowered V1 and Vr, where performance was doubtful. It kept the older types flying by making SOME effort when wet runways became accountable. It took care of the worst case, i.e. the accelerate-stop.
I don't know (J_T would) the first aircraft that had to fully comply with "True" V1s on a wet runway, but it's a pretty safe bet that all modern aircraft still in production have to comply fully.
In establishing AFM data for an aircraft's wet runway performance, there are basically 2 ways to approach the task -
(1) Apply a nominal reduction, like 10 knots, with the caveat that V1 must not be less than Vmcg, and determine the weight reductions that must go with the requirement to accelerate an extra 10 knots from the new V1 to V2 at the end of the TODA/TODR, OR
(2) Re-engineer the whole wet takeoff package from scratch (as opposed to applying adjustments to the Dry Takeoff data) such that "True" V1s (True Stop or Go speeds) are obtained.
The author of the offending text was correct for a bygone era, but out of synch with modern day requirements.
Regards,
Old Smokey