Early Norlins (though 1974) had what are referred to as 'transitional tenons' or 'modified long tenons'. A long neck tenon with the tongue portion cut off. I assume trimmed prior to assembly, rather than milled out during assembly. This tenon is visible in the neck pickup cavity. In 1975, along with the change to maple necks, came the short tenon, aka rocker tenon. Allowing for faster assembly, the neck can be 'rocked' slightly to achieve the correct angle. A short tenon is not visible in the cavity. With Gibson, dates are not set in stone. I've seen pictures of maple necked '75s and one '76 with trans tenons. I have a theory (but could be wrong) that Nashville never made a trans tenon Les Paul, that they all came from Kalamazoo.