I've never seen the word "free" when supercharging my S. I see the actual dollar amount when supercharging my 3.
When there were 40, 60 and 85 batteries, you had to pay $2,500 to activate supercharging on a 60 -- or it came free with the more expensive 85 (not free really since you had no choice but to pay for it). Plus, there were the 40's, which really were software locked 60's, but they didn't let people pay to unlock supercharging for the 40's. For the 60's they even had a sale on it once...
Those cars are still out there but you won't find one as a Tesla loaner.