Just to clarify on above response, my wife moved from F1 to H4 via consular processing (visa stamped) and applied EAD got approved in Dec 2017.
Her current EAD is valid till September 2020. In FY 2018, she moved to H1 in lottery quota and currently she had H1B visa stamped on her passport till Aug 2021.
She applied for H4 & EAD (COS) from H1 with my H1B transfer petition and its been 3months now. My H1B got approved in June after RFE.
Since the current processing time with USCIS are very slow, can she use the EAD which was approved in Dec 2017 to continue her work with out going for stamping? Please advise.