This post is more of a general discussion, not just a defect specific to grapes.  What would you do if you found a defect, like pictured here, that you were certain progressed into decay?  In this case, these seedless grapes show numerous discolored spots.  You can clearly see the discolored spots are eventually becoming decayed grapes, leading to wet and sticky berries affecting adjoining grapes.

The rule is simple.  You are to inspect the grapes based upon what you see at the present time.  Do not assume the defect will progress into decay, even if you are reasonably sure it will.  In this example you would report the percentage of grapes with serious damage by numerous brown discolored spots (scored against the 4% tolerance for serious damage), also report the percentage of wet and sticky berries and the percent of decay as you see it…..today.

I would guess this discoloration is caused by some kind of viral infection as the spots are definitely progressing into a decay.  Typically, discolored berries are usually caused by bruising or the grapes having been discolored by rubbing or abrasion.  Many times the discolored berries are simply the result of prolonged storage.  No matter the cause, the inspector should simply describe the defect and report the percentage of the defect found.