You 100% sure about this? I owned a 2013 Model S 60 and don't recall ever reading a 120k mile limit on the powertrain. I'm pretty sure that it was 8-year unlimited mile just like the other packs. I think that the only one that didn't have that was the original 40 because it was made prior to the warranty being extended to 8-years and unlimited mile powertrain and later it was extended to that car too.
Originally all Model Ss had a limited mileage warranty on the battery/driveunit. Then they changed it but only for the 85kWh versions. (The 40 and 60 kWh models maintained their limited mileage warranty.)
When they re-introduced the 60kWh version, using a 70kWh battery, it got the unlimited mileage warranty as well.