1. The reply is “No”. They cannot because employer B’s EB-3 was inherited by employer C, and you never filed a I-485 so that cannot be used.
2. Either go back to the first employer if they have a job offer. You can actually apply for a I485 without joining but this should be discussed with your lawyers in detail. Hence you could file for a I-485 based upon the job offer and I-140 which was approved through employer A but if you want to stick with employer C either you stick with EB-3 or you start another PERM application through them for your EB-2 categorization.
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Note: Unless the context shows otherwise, all answers here were provided by Rajiv and were compiled and reported by our editorial team from comments, blog and community calls on immigration.com. Where transcribed from audio/video, a verbatim transcript is provided. Therefore, it may not conform to the written grammatical or syntactical form.