It's the quality of the blade material.
do you mean numerical quantity or number of different patterns?
XX=20
XX = 20
The Case Copperlock started in 1997.
XX means twenty.
XX is the Roman numeral for 20
20
I think your are thinking of the Case RussLock knife.
The 62009 is a Case 1/2 Barlow knife.
The Roman numeral XX represents the number 20.
20