It says it there on the EAD. C 33.
That's all they need to know. If they don't know what that means, tell them to look it up.
__________________
Self filed AOS │Apps Received By USCIS - 3/18/19
│Biometrics Done - 4/11/19
Interview Scheduled - 4/24/19│Interview Date - 5/31/19│AOS Approval - 5/31/19
Permanent Resident Card Received - 6/8/19