This zero turn has skid plate under oil pan, and only one plug accessible, and operator's manual shows only one plug.
Have been running a G5200H for 31 years with same basic engine, only 16HP. Changed oil at the beginning of every season in it and never had this happen. On G5200 oil on dipstick not quite as clear as when it came out of the jug, but not almost as black as oil drained from engine.
On the zero turn the engine was allowed to drain for over an hour with the oil filler cap removed while I lubricated everything else.
After getting the high mark I let engine idle for five minutes and waited 15 minutes for oil to drain back down. Not quite as high as previous check, but still 1/2" or so above full mark. By measure from markers on 1 gallon (Shell Rotella) oil jug I put 3.5 quarts in it.