Quote - Is it possible she altered the gamma on an image, but was not aware of doing so? Perhaps - which is why I said, in my first response to the issue, "Or for you to realize that you changed two things and assumed that the other thing was unimportant"

My guess is that the Vendor added gamma to the material already which is why there are differences in the render even when the Gamma Correction is changed.  It may also explain why someone would say they made no changes to materials, not realizing that the vendor made the changes already. Some of my character skins have gamma changes but the only way I knew was because I used the Image Gamma script. (better than hunting for nodes).  So I can see where the confusion would come from since Gamma Correction isn't the Same as the Actual Gamma.

But the first assumption for many people who aren't familiar with gamma may be to use the Gamma that Monitors (Mac vs PC) opperate at it.  I think Photographers have a better idea when it comes to gamma since it's a common edit feature for photography.