Get a grip thing! If you are looking at the original Cessna weight schedule, as you claim, it should be written on parchment!
ALL AIRCRAFT GAIN WEIGHT OVER THE YEARS - THEY DO NOT LOOSE IT!
Are you part of the 'best of the best'? Without knowing what 'best' is?
There is a compelling reason for microlights to be re-weighed every 5 years. If you are flying an aircraft with a 20 plus year old weight certificate it is a work of nothing more than historic interest.