I found the following info:
"移民局不接受以下几种情况的I-140加急处理申请:申请人有另外一份I-140申请还没有被处理(STILL PENDING)"
at http://goabroad.sohu.com/20060930/n245620689.shtml
My question is, 2 I-140 have been sent, all are pending. If the suspension of I-140 premium Processing is lifted in the near future, I am afraid I can not apply the premium for one I-140 if I have another one on pending. Any professional suggestions? Thank you very much for your help.