Keep in mind that back in the 60's and 70's, the "published" useful loads were for the aircraft with "standard" equipment. In an effort to make the planes appear more capable than the competition, the marketing folks convinced the designers to make "standard" pretty skimpy -- like what was required by 91.205(b) for day VFR and that's about it. On many planes, that meant no radios, no external lights other than a rotating beacon, no vacuum pump or gyro instruments, etc. In those days, a typical plane left the factory weighing 75-100 lb more than the "standard" empty weight in the marketing material and owner's manual, and that meant taking a 75-100 lb bite out of the "published" useful load.
Today's planes typically come fully equipped for night and instrument flight, with advanced displays and systems along with much better creature comforts, and so they have much lower useful loads out of the factor than the same models did 40 years ago even with a typical set of optional equipment.
In any event, if you are looking at buying a plane, take a good look at the actual W&B data for that plane so you know what you're getting, and if you b want to know what you've got, get it weighed. That said, based on some weigh-ins in which I have participated with typical light 4-place singles, expect that weighing to give an actual weight of around 1 lb more than the paperwork says for each year since it was last weighed.
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