Jeff - I believe that the percentages you are referring to were in relation to a handicap system. You will find quite a few boats sailing during the later periods with percentages relating to the time that would be added to their final elapsed time. It does not relate to a class per se.
In terms of the class designation P - 1, Nellie may well have been the first Universal boat rated as a P-class boat. Look at the Skene "Elements of Yacht Design" and you will have find some information on how various class were designated. Early in the Universal system, yachts (especially gaff rigged boats) tended to be at the upper end of sail area and shorter in waterline length and smaller in displacement. By the 1910 or 1911, the boats moved towards the other end of the rule envelope, that is bigger displacement and smaller sail areas. In summary, given Nellie was launched right around the time that Herreshoff put forward the Universal Rule and many yachtsmen would have given the "new" rule a try, I think it is quite possible that Nellie was the first rated P-class Universal Rule boat. She may not have been designed with the rule in mind, but that does not take anything away from her being the first.
Hope that helps.
Glenn
