For what it's worth, here is a section in "Hurrel's Hollywood Portraits" by Vieira.
"Nineteen thirty-one was approaching and George Hurrell was runing out of orthochromatic film. He could have ordered more, but the range of film stock now available in the newer panchromatic was too tempting. (It included Par Speed Portrait, Portrait Pan, and Super Speed Portrait). Panachromatic means "all colors", and indeed this film saw the entire spectrum. The ortho film that Hurrell had used for portraits of Joan Crawford (1930) and Norma Shearer (1930) had made their eyes too pale and their lips too dark. Hurrell took a chance on Par Speed Portrait. He found it's tonal rendering an improvement over the ortho; it gave skin tones a creamy rather than burnished look, as in the Norma Shearer portrait for "Strangers May Kiss" (1931).
Pan Film, introduced in 1928, was easier for both photographer and subject because it was faster than ortho film. This increased sensitivity to light allowed Hurrell to shoot at exposures as short as one second. He couldn't shoot much faster than that, though, because his beloved Verito lens had to be closed down further to get those sharper edges he liked. Instead of using a faster lens, he poured on more light. In order to do that, he adopted a radically new lighting scheme. With it's innovation, he began his third period of artistic development."
It seems that after about 1931, Hurrell switched film types and went away from Ortho film. At that time, he also changed his approach to lighting (using higher powered lights) and started using a 16" Goerz Celor lens at least for some of his work. So it looks like at that time, he was less worried about the film type and more worried about light and lenses than before.