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Hi, Dan. The Apple part numbers supplied were used to order exact replacements now in my MBP 15. I have also checked them against Apples official Screw Chart for the MBP 15. I am very sorry you have been supplied the wrong screws but the part numbers listed are correct.
I located the part number for the 2 easily stripped screws in this step. The 3.9mm is Apple part 922-8974 and the 8.6mm is Apple part 922-9107 pbparts.com has them available for $2 each.
Hope this helps, it was not easy to track down.