Don't know anything about raising your deck, but what you say seems lower over the 12 years is true, likely due to the wheel bushings/spindles wearing & the deck hanging brackets the same, you get a wheel off the ground & give it a jiggle, I bet it is looser than you ever imagined.
I did find out how to raise the deck front and rear at the same time.I have a 28inch 2006 rear engine snapper rider. First remove the plastic deck cover it has 2 short screws in front and 2 longer bolts in the rear. Once that cover is off you will see on the right a long threaded bolt
With a 9/16 nut on the end,turn that nut with a 9/16 socket.Turn that nut in too expose more rod threads maybe about a 1/4 inch.Take note of your starting point,I have now a taller cutting height.You also have to readjust the 2 chains that bring up the rear of the deck.My deck is slightly higher in the front and that’s in the snapper owners manual.The raising of the deck is not in the manual.
