I believe you'll find most of the cruising boats out there ended up built well over their designed weight. The weight is usually calculated by the designer/architect on the drawing board. Very few builders were careful or consistent enough to turn out boats with the perfect mix of glass to resin, keels that weigh exactly what they're supposed to or even build two units of the same boat in exactly the same manner.
The serious racers are usually pretty close, but a 20 year old production cruiser is anyone's bet. This is why you'll find that there can be two boats from the same builder, of the same design, that have differing performance levels or characteristics.