Great Black-backed with Pseudo-Mirror on P8

Not too many large white-headed gulls develop a 3rd mirror on the 8th primary. Common Gulls regularly do, but Great Black-backeds??

Olsen and Larsson note that about 10% of males and less than 1% of female GBBGs develop a small mirror on P8 (~35mm in males and ~10mm in females). Simply put, it's not commonly seen by most field observers. So I was super excited when I found this bird circling "The Devil's Dance Floor" on Appledore Island recently:

Adult GBBG with triangular-shaped mirror on p8 and two white tips to p10 and p9. Notice the relatively thin white tips to the inner primaries when compared to the mid-secondaries. This is quite different than Western, Slaty-backed and Kelp Gulls.

I'd give up chocolate for the rest of my life to know how old this individual is and how this primary pattern progressed as it aged.