I think it was awarded when they weren’t sure if it would be May or August, but they knew either would work.
Incidentally I doubt they’ll ever go back to Harding as they have the PGA/Ryder Cup deal with Olympic. One can imagine this PGA might have been at Olympic if OC has known they wouldn’t be in line for another US Open in reasonably short order after 2012. I think the PGA, at the time, saw Harding as their only available option to play around SF.