<font color="blue"> They were both rear mount Bush Hog finish mowers. Both were rated well past the PTO horsepower of the tractors. I considered this a cheap slimy sales ploy to make the one tractor look like a better deal.
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I may be misunderstanding what you wrote, so if I am off base, then I apologize up front . . . but the gearbox on a mower (or tiller, or whatever) is typically rated for a maximum HP rating. Different size mower decks can use the same gearbox. So it is very common to find a 35hp gearbox on a mower deck, with that deck being recommended for ANY size tractor up to a 35 pto hp.
That does not mean that a 24hp or even 30hp tractor will have enough power for the mower deck.
What it means is the mower deck is capable of safe operation with a tractor up to the gearbox rating.
Now if you want to mow the lawn with the tractor, there is a common belief that you need 3 to 5 pto hp per 12" of mower deck. That has been posted on this site and others numerous times, I have NO CLUE if it is true. But using that criteria, then a 60" mower deck is the MAXIMUM size you'd want on a TC24D. I happen to use a 60" deck on my TC24D and it works great as long as the grass is not long and wet, at which point it can bog down the tractor a bit. It mows through "normal" grass cutting chores without any problem. So in theory, a TC30, which has a few more PTO hp should be able to run a 72" deck while the TC24D would be limited to 60". That doesn't mean your dealer would recommend these sizes, it is just a rough approximate.
Again, if I misunderstood your post I am sorry. But if I understood it, then I hope this may clarify why the same deck might be on both tractors.