“…We also apply our proposal to the SW curves for classical non-simply-laced groups obtained from string theory constructions with orientifold planes [15,41,58]. As a byproduct of our construction we show, in type B n , that the curves proposed by [15] from an M-theory uplift of the Hanany-Witten construction with orientifold planes correctly reproduce the instanton prepotential for SO(2n + 1) gauge groups; and in type C n , we confirm a tension between the results of [15] for n = 1 and more recent proposals of Sp(1) curves with discrete θ-angle at θ = π in [41,58]. Although the two curves are closely related, and their periods are shown to be annihilated by the differential ideal generated by the second line of (2) for the same choice of structure constants C k ij , in this rank-1 case determining the full expression for the periods requires fixing a finite-dimensional ambiguity akin to imposing a quasi-homogeneity condition as in the first line of (2): our calculations show that this is done differently for the curves from [15] on one hand and of [41,58] on the other, ruling out the former and confirming the correctness of the latter with a direct prepotential calculation.…”