I would think if it was fluorescence causing the haziness, clarity would not be relevant? Anecdotally I hear fluorescence is more likely to cause an issue in DEF colors than lower colors, dunno how true that actually is though.
All of the labs to my knowledge (GIA,AGS,IGI do) offer the submitter to ask for it to regraded if they disagree with the grade for a fee of course.ctd.
I suspect that none of the labs offers a formal procedure to contest grades; on the contrary. I do not know to instigate blind re-grading, except by another lab.
Tough, this ,(