aterpster,
Thanks for the link. I still disagree with you though, based on the wording in 97.3
Aircraft approach category means a grouping of aircraft based on a speed of VREF, if specified, or if VREF is not specified, 1.3 Vso at the maximum certificated landing weight. VREF, Vso, and the maximum certificated landing weight are those values as established for the aircraft by the certification authority of the country of registry.
The way I read it is that if Vref is not specified, then you use 1.3*Vso at MLW.
My understanding of it in practical terms is that a light aircraft which doesn't have a published Vref (eg C172) would use 1.3*Vso at MLW, and so would always be in the same category. A larger aircraft has published values for Vref, and so the category would depend on weight.
Am I way off the mark here? If I'm not mistaken, you have a background in procedure design, so I'm interested to hear your take.