I am missing one stamp in my passport for entry in US. And worse is this is the stamp of my entry after 5 months out of US (the only prolonged period). So if someone looks at my passport would say I was out 7 months (because 2 months later I was out again). I gathered all documents from that period (rental agreement, ID issued at that time, hotel bill, etc.), but is it enough? Can I go to the airport and ask Immigration to stamp it by providing them proof that I entered the country? I don't understand why they wouldn't stamp it in the first place. I had 10 trip outside US and that is the only trip I am missing.