I would think some obvious clues would be, serial numbers notwithstanding, bridge pickup position, truss rod access and type, not to mention that a 73 probably had reverse gearing on the machine heads. Paint type would also be a clue.
Just to clarify- 1973 did not have reverse tuning machines. The reverse tuners went away on Jazz basses between '65 and '67. Reverse tuners are easy to spot since the original Fenders all have small clover ears and rivets attaching them to the tuner post.
Of course, after market tuners and vintage reissue tuners may or may not be reverse , so beware of tuner swaps.