I entered the US last year (2010) in mid November on my Italian passport with the WVP through transit onto Mexico where I stayed just over two months and then returned to the US for transit back to Australia in January this year (I therefore spent a total of about 2 months and 2 weeks in North America - under the 90 day limit).
My question is: As when I departed the US the final time in order to go back to Australia I didn't have to talk to any immigration officials nor hand in any tourist card or documents and so how would the US have a record of when I left the country? Also to make things more complex I self-checked myself in for my flight to Sydney (in LA airport) and in order to check in I had to use my Australian passport (for Australian visa reasons) so therefore I checked in to my flight out of the US on my Australian passport and not my Italian passport in which I had been registered under the VWP and in which I entered the US (and also mexico) in the first place. So basically would the US have a record and/or knowledge of me leaving the country in January this year? Would the US know that I who entered on an Italian passport was the same person who left on an Australian?
I am just worried as when I wish to return to the US for tourist purposes in the future if they will think I never left the country and that that I stayed over my 90-day period in North America.