RSA grant with 83(b) then repurchased by company, capital loss?

I previously received a RSA stock grant from my employer and filed a timely 83(b) to accelerate the taxation of that grant into the granting year.

 

I paid $0 for the grant and recognized the $YYY fair-market value in that year as regular income.

 

Unfortunatly, I left that company before the grant was fully vested.  25% was vested and I still own that, however the remaining 75% was repurchased by the company for $0 when I left.

 

How do I report the remaining 75%? This seems like a capitial loss since the basis at FMV was declared due to the 83(b) when granted then the company purchased it from me for $0.

 

In summary, that 75% was:
* I paid $0 out of pocket
* It had a fair-market value of $XXX due to 83(b) at time of grant
* That $XXX was included in regular income and becomes the basis for any future sale
* It was then repurchased by the company for $0
* Capital Loss: basis = $XXX, proceeds = $0, gain = $-XXX

 

Can this repurchased unvested portion be counted as a capital loss?

 

Because no 1099-B was involved, do I need to provide any supporting information? I could see how this would look unusual.