A lot of information is stored in the parts list of a drawing/assembly. This information cannot be used in naming components within this drawing.
Example
In my assembly I installed a total of 6 pieces from position 6 (Bild 1).
In the assembly I isolated position 6 and inserted it into the drawing to create a manufacturing drawing for this component (Bild 2).
In the "Format Text" window I do not have the option to select this number from the parts list (Bild 3).
This would cause the number in the component label to automatically adjust when the number in the parts list changes.