Does anyone know what is the difference between the flatness callouts in the attached image?
The one on the bottom is calling out the flatness of the surface to which it is pointing.
Regarding the one on top:
"Where flatness is associated with a size dimension it is applied to the derived median points, or to a boundary of the feature when the maximum material condition or lest material condition modifiers are applied."
-From my GD&T class book (I don't think I've ever seen this in real life)
That said, the callout on top doesn't look correct to me, it should probably be under the dimension, not lined up with the dimension line.