Riding Lawn Mowers

I am a recent widow and am trying my best to be self-reliant. That means I sold my older, larger lawn tractor and bought a Husqvarna YTH24V48 that is more manageable for me. I was told to change the oil after using it 2 times. I did that today with my son-in-law giving me guidance so I will be able to do it myself the next time.
The manual says use 60 ounces of oil if you are not changing the filter. The oil dipstick said the oil was at the correct level before I changed it, but I only got around 40 ounces of oil out of the machine. When I refilled it, I kept checking the dipstick to make sure I did not overfill. At 40 ounces it again showed correct amount. What in the world is going on? That's a big difference from 40 ounces to 60 ounces.