Something escapes me on the mechanism adopted by some fonts to manage proportional and tabular numbers.
GaramondPremierePro does not seem to present proportional uppercase numbers. It contains the glyphs of the numbers (slots from 48 to 57) and those of the numbers .fitted (slots from 63033 to 63041 + 63196), but all the uppercase numbers have the same width (including the bearing, all are 486 pt), so in fact they are tabular as the .fitted ones.
However, if I compile with LaTeX I add the <lining> option, the numbers become proportional.
Did I look badly or is there some mechanism I didn't catch?