I had a I140 approved through Employer A in the month of June 2015. Moved to Employer B (Feb 2017) using the approved I140 by H1b Extension. Got an extension till DEC 2019. Employer B has not started the GC process yet. Now, intending to move to Employer C, can the Employer C file a H1B Extension based on the approved I140 (by Employer A) as it is more than 180 Days when my I140 was approved through Employer A and as far as I am aware, USCIS will not cancel/withdraw I140 after 180 Days of approval ? But my awareness on this matter may be limited hence seeking advice from experts. Please comment/suggest.