Joined new employer briefly, went back to original employer. Risks for stamping, extension, amendment?
While working at Company A on an approved H1B. Without resigning from Company A, they join Company B which had filed and received an approved H1B transfer. After working at Company B for 1-2 days, they resign from Company B and continue working at Company A (never left Company A, never had a gap).
Company A's H1B petition was never revoked or withdrawn — it remained active the entire time.