I have a 1992 dodge stealth that has been sitting on Jack stands since I could walk, so more or less 14 years . I'm a junior in high school and my plans for the car are to get the car back in "running" state . Would this long term Jack stand period cause any body or chassis damage if jacked correctly ?
Time will be the real problem - fluids evaporating, degrading, leaving residues, metal rusting due to humidity etc etc
It depends on how, or if, it was prepared for storage...
But leaving on stands should not increase the issues.