Lay them out and look for the obvious...... Tears, abrasions, etc. Then check the stitching to be sure its all intact. Even if it is, run your fingernail over random places. If UV damaged, some fibers will come off under your finger nail. Have them re-stitched or inspected by a sail loft.
If good structurally, the only remaining problem would be they have become mis-shapen. This would degrade performance. Its unlikely you would have blown out sails without other signs of age though.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.