I'm not going to get into engine specs, or paint and interior. But, one easy way to tell, if not the exact year, at least a ballpark figure of a Beetle. And that would be the taillights.
Another was by the rear window(s).
Also the badges can help to identify the year. (As long as they are still stock.)
Another way would be the head lights. You can tell if the Beetle has headlight lenses, that it would be pre-1967 and earlier.
And it will have non-covered headlights with benzels, if it's post-1966.
Any beetle without a dash mounted gas gauge would be pre-1962.
Any beetle with front struts is a Super beetle. And would have a curved windshield and dash after 1972.
Also the Super allowed for the spare to lay flat allowing extra space in the truck.
In '71 VW added a padded dash. The Super Beetle also had the flat padded dash and the half-moon steering wheel.
1973 Super Beetles had a curved windshield. And a new steering wheel was added to both the Standard and the Super Beetles.
Also the generator was replaced with an alternator in mid-'73.
Moon vents were added to increase fresh air flow in 1971.