one thing is strange... why the amount of oil added was different every time. that's strange.
Lexus change to WS ATF after 2004. The WS ATF don't need to change as often as old type IV. In the US, Lexus said it will last as long as you own the car. which means you never need to change it.
The new type of transmission is sealed. I heard from my local Lexus dealer that if you haven't change it, you do not need to change it at all.... however, ONCE you change it, you will need to keep changing it. Because the transmission was sealed from factory, there is no air going in and the oil will not oxidation or absorb moisture from air.
I think BMW was the first menufacture who come with the "lifetime" ATF. I have the first generation of that kind of ATF. my car is a 1999 3 series. it has over 130000 miles now and i have NEVER changed ATF. My car is still running great.