My guess is that the folder numbers are indicative of ad design and placement, 7751 being that specific ad for pickups, and 7732 being that specific one for strings. Letters indicate where the ad was run. It doesn't look like a code where "A" = Guitar Player, etc., but likely first placement, second placement, etc.
If you responded to the ad, and included the folder number, Guild could then track how effective various advertising vehicles were for specific products.
If you responded to the ad, and included the folder number, Guild could then track how effective various advertising vehicles were for specific products.
