Marginal Revolution has a discussion of the history of grade inflation.
I was interested to read that the students who were let into the French colleges, without the grades, did benefit from subsequent higher salaries. I didn’t know that part of the story and it does add a bit to the idea.
I do all I can to help my students raise their grades, so I can certainly see how adjuncts end up with higher grade inflation. I hope I am not guilty of that. I have been a hard grader in the past. I don’t think it has changed that much. I am just willing to work with my community college kids to give them more of a chance.