My parent went back to China 2 years ago, and they just told me that they found they didn't return I-94 (hind in one evelop) and they didn't keep their fright ticket either. Since we hope to invite them to America again, we hope to know whether there is a trouble in the visa. One more thing, I heard if they change a new passport(say the old was lost), INS can't figure out when did they leave, is that true? appreciated for any suggestion.