Jeff, I hate to shoot you down, so I'm not.
That's most likely correct. The knife has probably been sharpened enough times that it is getting thicker behind the edge. This is where our argument of "perceived sharpness" vs "actual refinement" comes into play. I have handled quite a few used Globals with this problem before.
Since you say that your Global is no longer holding an edge I will assume you know how to sharpen? If so, then what kind of sharpening equipment do you currently have?