I think that coin was messed around with, just prior to submission to the
TPG. Then, even with a decent seal, the degradation continued in the holder - we see the same phenomena with copper re-toning, carbon spot formation, etc. Remember that even ICCS flips are not impermeable to moisture, this coin could have been put in a really humid environment. Currently, the coin should be commented as 'corroded' or 'unusual surfaces'. Normally, I don't hesitate to dip mint state Elizabeth II coins, but not even dipping will save that coin now. Despite the wonderful reverse, it only has two useful purposes now: 1) a Whitman folder piece, whereby you don't have to see the reverse, and 2) .800 silver melt.
That said, I think your coin would be a fantastic addition to a grading course that several of us in the Ottawa Coin Club are designing. Please do not cut it out of the ICCS holder. If you want to discuss further how this coin could be of educational value, obviously, we have to take this offline...