This is certainly up for debate and an interesting topic, but I disagree that factory record alone determines the grade of the gun. We have no reason to believe that every employee in that era was inherently better than what we are experiencing in today’s work force, iykwim.
True story. I once owned an F250 that coded out to the insurance company as a top of the line Lariat edition when it was actually a work truck XL. Just because the factory vin records said it was a Lariat Edition did not make it more valuable. How about this angle - how many guns were recorded in a higher grade than actual? Imagine yourself paying market price for a grade 3 10ga with simple field locks just because it “lettered” as a grade 3.
Just a few thoughts. Value? As always...What the buyer will pay. Or is it what the seller can fetch?