Current GC employer is A and I want join employer B. I-485 currently pending with PD 12/2004 EB-2:

1. The SOC code for the job mentioned in my Labor is 15-1032 (software engineer), whereas, the job that I'm getting is 15-1099 (software test engineer). Since the first 4 characters of the SOC codes are similar, do these 2 jobs qualify for portability under AC-21?

2. Lets say, I decide not to use AC-21. If I leave employer A and join employer B, and later I get a RFE for employement verification, can I then get an offer letter from employer A, saying that they are willing to hire me back once my I-485 is approved?

3. If I dont get offer letter from employer B, what are the other ways to prove my current job with B is similar to the described in my Labor cert, if I want use AC-21?