The EB1A and NIW applications were both approved and I got my green card via EB1A at first. May I get another green card via NIW?

I appied for US green card via both EB1A and NIW categories. The two applications (I140) were both approved. At first I got my green card via EB1A category but then I stay outside US for more than 2 years —- so it seems my green card became unvalid.

Now I received message from National Visa Center (NVC) about my NIW green card process and asked me to submit post-I140 documents and to continue my application. Can I do that, as it may confilict with the green card I already have in hand (the priority date had been used by the first green card process)? Many thanks!