What you read is correct, assuming no leaks the fluid level in the master cylinder reservoir increases as the clutch wears, which is opposite of how the brakes work.
If you see no signs of leakage at the master cylinder, closely inspect the fluid line from the master cylinder all the way to the transmission side cover for any signs of a leak. Some lines have been known to develop leaks from the rubber inner liner into the braid layer. You will have to look closely with a good light but if that it what happened it should show up. If inspection of the M/C and the line shows nothing, then you need to remove the trans side cover and inspect the actuator (slave cylinder). If a seal has failed, you can get a rebuild kit, P/N 36822-04, MSRP $39.95, from a dealer.
Jerry