t(21) in {4,5} is the smallest value not determined by EHT91's stated results, and the miss is razor-thin: Theorem 6(I) at t=4 needs window p(21,4)=61 while 3r-3=60, Theorem 6(II) delivers only (59,1) not-arrow 4, and no member of the H(r,k,q) family with k-q >= 4 satisfies the local property at r=21 (exhaustive check over all admissible (k,q) via an exact complement-covering span criterion, itself validated against four exhaustively-computed instances). The undetermined set below 60 is {21,26,31,36,37,41,42,46,47,51,52,53,56,57,58}.