All About Pocket Knives

Picked this up at a garage sale for five bucks. Can anyone help date this one? I know the early ones had micarta handles but they had three pins. This one has micarta with two pins. The Buck script puts it before 86' but I'm wondering if this is an early one still using 440 steel.

The Micarta scales mean that it was made prior to 1981, give or take. There doesn't seem to be an agreement about when the switch away from Micarta happened, or whether it was done at the same time for all 500 series knives. As far as I know they were introduced with 440C steel around '77, and would have graduated to 420CM in the early 90s with the rest of the lineup.

The early 500s are hard to date with any precision.