Yeah! you are right
Actually, my case is very complicated.
I filed my GC (labor certification and 140) through company A under EB3 category. In the mean time I left company A and joined company B even before filing for 485. Ofcourse company A promised to continue my green card. In June last year when EB3 became current, I filed for 485 with a employment letter from copmpany A.
Then my attorney suggested that I should take advantage of the AC21 rule (change of employment after 180 days) and in Feb this year I send a new employment letter to INS from company B. My job description is still the same.
Now, only GOD can help me!!!!!!