Know if they were supposed to be a matched pair? Guessing the one with 7.9 ohms is defective but I could be wrong. Could be half of the diaphragm is open. I would measure the one that is 3.9 ohms and see if it looks right as far as frequency response.
They made both 4 and 8 ohm diaphragms for different models over the years so one was repaired with the wrong impedance diaphragm.