回复:priority date and receipt date
Priority date is the date when a person submits his LC. For those without LC, it is the date when I-140 is submitted. If the LC or I-140 is approved, you own the date no matter how many LCs or I-140s you later submits. If you use other people's LC to file 140, it is the filing date of that LC (this pratice may change end of this year)