To me it looks like the nibs are still there, just very shallow
Those are not nibs! Looks to me like during a re-fret, the nibs were cut and the old frets removed then the new frets were very carefully cut to slot back in tight to the binding. Nibs come up the side of the fret; the picture does not show this. It is also possible that the nibs were filed off during a redressing of the original frets. Some guitars suffer from nib gaps that catch the high E string. Perhaps this was the case with this guitar and a previous owner simply cut and filed the nibs off; this would also explain the severe wear of the frets if they are original.
