OPT EAD approved but card not received yet; employer wants me to start next week and ready to accept approval notice. Violation?

My question is similar to another recent post and is regarding OPT EAD authorization process. My OPT EAD application has been approved and I already have the approval notice with dates starting 12/22. However, I am yet to receive my EAD authorization card. I have a full-time job starting next week and the employer has notified me that that the approval notice can be used in lieu of the physical card which I can show once I get it. Will it be fine for me as an individual to start next week if the employer wants it? OR should I back-out of the offer and wait until I get a the physical copy of the card. I called USCIS (spoke with an officer) and was informed that approval notice can be used in lieu of the card as my application has already been approved. Looking for advice!