The thin was obscured by the thick paper covering
that area in the back. The expert I spoke with said that
adhered paper would result in points being deducted
and it was wise to remove the paper obscuring the back.
It was impossible to detect thin with paper adhered.
I am quite sure I did not cause the small thin.
The PSE deducts 15 points for small thin but will add
10 for for color freshness such as this stamp has.
Take a look at the back of the stamp and thin
Is not visible against black only detected in fluid.