QFN 5mm x 5mm Footprint Dimensions?
The reference for this part is at the corner where planes A B and C intersect. The device package has a tolerance in size of +/-0.05mm.

You can assume the pads are nominally centered on the nominal 5mm dimensions. 

If you are trying to figure out the tolerances it gets a bit more complex, but I don't think you care that much about the location of the package relative to the pads. If you were to check the dimensions you would use those planes by putting the part in contact with precision surfaces at those planes.  

It looks to me as if the pins are guaranteed to be within 0.1mm of the nominal positions relative to the A B C corner and within 0.05mm of the bottom plane.  

That is a pretty fine-pitch part- 0.35mm. Ouch. 

There is a drafting principle that redundant dimensions should not be included.