They are described as Membership Units (LLC filing as a partnership for tax purposes). An 83(b) was given to me and it was filed. It showed a valuation of ~$125k. The units are unvested but would have vested over years and some other performance obligations.
There is nothing in Box 11 on the W-2 but I believe that is more to do with the company and their poor administration of these events - i.e., not understanding how to do this in the HRIS system.
I withdrew from the membership as I saw that they were not living by the agreement (not reserving for tax liabilities as described in the operating agreement). I was employed when I withdrew but have subsequently left the business in early January.
It seems like I have to pay the income tax on the $125k but ultimately have no other recourse to record the withdrawal or be able to reverse the income tax impact.
