Nishu - If you lose some Notice from INS, as far as I know, you can always ask them
to mail another one, explaining them that that you did not receive it. These guys are fair in that matter.
I am not sure about receipt date - but if they say that they received it on X date, that is it. For eg. I mailed my I-140 in November. But I got a receipt date as if it is in Jan (subsequent year) - and the application will be (and was) processed according to Jan only not Nov. So, just wait for Notice and see what it exactly says. By the way where is your updated tracker ?