請教小白兔: 新申請EB-1A 可否利用原來NIW 的485

Xiaobaitu:

I have concurrently filed my NIW 140 and 485 last september. 140 has been approved. Since Chinese EB-2 may face further retrogression, I want to re-apply for EB-1a. Here is my question: Can I just file I-140 for EB-1a and if it gets approved, can I switch the old 485 for NIW to EB-1a and keep the priority date or I have to file a new 485 for EB-1a? Thanks a lot for your help!!