Lol duh! Even if the butt was the same width on all 4 nut width choices, the slightly different nut widths would create slightly different angles (Trigonometry) on the sides of the neck, so the sides of the neck pocket would need to be angled accordingly. (I’ve read Tele neck pockets have slightly angled sides and aren’t totally parallel to the centre line ...) So you would in theory need a ‘B’ neck pocket to pair with a ‘B’ nut width. Maybe they used this stamp system just in the 60’s? Otherwise it could be a ‘B’ width nut from 1957/67/77 etc. right?!