As a follow up:
My Nitto Ridge Grapplers were installed at 110,299 miles. They were swapped out at 169,023 miles with a measurement of 5/32 all around by the paperwork, 58,724 miles on them. I will say I did not feel the tires needed to be replaced, I just wanted new tires.
My Toyo AT IIIs are listed to have 16/32" when new by the Toyo site.
When rotated with 6,677 miles the measurements show 14/32" all around.
When rotated with 19,033 miles the measurements show 11/32" at three tires, one tire is 12/32".
While at Discount Tire today to see when my rotation was due they are now using a different device to check the tread depth. Pretty cool little handheld device that must be an optical scanner. As the MGR passed the device over the tire it took a reading. He stated the device reads from side to side of the width of the tire. This gives them a better idea as to how the tires are wearing. Without being able to give me a printout ( no rotation today ) he said at 21,857 miles all tires were in the 10-13/32" range across the treads. There is a way to import that info from the device when they do a work order. So they are able to give the owner's a copy for reference.
With this new device I know the new numbers and old numbers may seem a bit off but in the long run it will even out as far as info to share.
So if I were to take the low range now of 10/32" measurements at 21,857 miles across all tires compared to the as new 16/32" by the site that's not too bad for me. I could go with the higher end, but that's not reasonable with a new tool being used to check the tread depth. Let's see what happens!