The AC21 only mentions 'similar position' and 'if the I-485 has been unadjudicated for 180 days or more'. The final regulations for AC21 have not been established, so each case is going to be treated individually.
You'd certainly want to consult your lawyer. I believe with L1, you don't have to go through Labor Certification, and now with AC21 you are going to enter an open market. My feeling is this is irrelevant, but your lawyer should know how to deal with this issue based on actual AC21 experiences.
