Bob:
Quite simple actually. Max gross weight doesn't change, but as gliders
get older and equipment is added or someone paints over the old gel
without grinding down to the glass, or grinds down to the glass them
repaints/gels and profiles the wings, they seem to get heavier. More
so if some repairs have been made. George is correct in that the glider
is most likely stronger, but increased strength does nothing for the
useful load. If the weight of the glider increases, but the max gross
doesn't then what suffers? The useful load.

Regards,

Billy Hill