I'm stumped. 3rd child arrived a few weeks ago and I decided to investigate putting a 3rd row in my 2000 Yukon Denali. After doing some homework and searching for seats, I located two NOS seats here in the St. Louis area and purchased the seat mounting hardware from the GMC dealer where I purchased the car new in 2000. I pulled up the rear carpet this evening only to find that my car is not in fact "pre-drilled and tapped" for these seats. All indications were that these seats would work in any 2000 to 2006 Yukons, Tahoes, or Escalades. Why don't they fit in my car

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The door sticker shows my car as being built at the Arlington, TX plant in Sept of 1999 but it's registered as a 2000. The car was stickered as a 2000 but I'm starting to think I really got a 1999 model year car from the dealer. Any input or help would be much appreciated. Thanks,