if your EB3, you should have LC filed to SWA(state level). the date they recieved your LC application is called Priority Date. or L.O date (it should be marked on your ETA750A form, at the lower right corner).
Not related to any 140 stage unless you are using someone else approved LC to apply for GC.
if you are using someone's approved LC, the date you filed 140 is your priority date.
if you don't use LC to apply for GC,e.g. EB1 or EB2, your priority date is the date INS(USCIS) recieved your 140 application, which is provided in your 140 recived notice.
Not related to any 140 stage unless you are using someone else approved LC to apply for GC.
if you are using someone's approved LC, the date you filed 140 is your priority date.
if you don't use LC to apply for GC,e.g. EB1 or EB2, your priority date is the date INS(USCIS) recieved your 140 application, which is provided in your 140 recived notice.