Just contacted Rick Hunt, the Engineering Technician at EMG Pickups, and newer HZ's have barcode stickers on them telling which ones are which.
Back in 02' when my vipers were made, ESP bought them in bulk, no stickers on them so the only way you can be sure of telling older HZ's apart is putting a meter on them and referring to the spec sheet.
Sadly enough EMG has no further info on guitar makers and which type was used which year...
Very nice guy, and got back to me quickly.
Just thought you would like to know what I found out.