3.1 Scope, states in part that all prequalified WPS's shall be written. In order for a WPS to be prequalified, conformance with all the applicable requirements of Section 3 shall be required. It goes on to state that for convenience, Annex H lists provisions to be included in a prequalified WPS.
These provisions are shown in Annex H as a list of subsections that the prequalified WPS must address. One provision is 1.2 Limitations, which states that when metals thinner than 1/8" thick are to be welded, the requirements of D1.3 apply. Since there is a minimum thickness indicated, but no maximum thickness indicated, I interpret this to mean that 1/8" through unlimited thickness base metals are prequalified for fillets (excluding fillets made by GMAW-S), provided the criteria of Table 3.1 is met. Also, as Bill Mc stated, the welder qualification tests determine the qualified thickness range, which is 1/8 to unlimited, regardless of the fillet test option (Table 4.10).