So technically a 7000 lbs tandem axle trailer can have 8000 lbs on it including the weight of the trailer if you account for about 1000 lbs worth of tongue weight? Wouldn't want to put that much weight on it too often thoughNo. The trailer appears to have no issues at all whether its two or three mowers back there.
Remember, some of that weight is on the tongue. I usually put the 272 up front. With the wide 72" deck, it's just easier to be tied down to the front of the trailer instead of the sides. So I estimate about 1000 lbs on the tongue. So even when fully loaded, the axles are only carrying about 5500 lbs. together.