Stamps on the passport are the only proof I can think of. They've also asked for calendar "dates" where time was spent since 18 years of age. It is so hard to provide this level of detail. I had provided the detail in a year format (no months and days).

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George Malley: Hey, would you, uh, love me the rest of my life?
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Took me 3 days to figure out every detail for my folks, I have from date to date - not sure what they will do with this info? do they cross check, I mean unless you the person who has traveled, its impossible to tell from stamps AND stamps can be incorrect ( I have had wrong year inserted in mine back in 2000 at Montreal Border )

How many passports do your folks have and are you in the same situation where they have lot of travel history?

I am worried that if I should send fathers FBI even though he hasn't been there more than 6 months

So tell me G13, they already have passport but yet they ask you to show it ie., they couldn't figure it out
You think this is because you gave year instead of exact date and went over?

Greg38: Yes, my parents have a lot of travel history, passports crammed with stamps over each other, some of them difficult to read / photocopy. They don't have all their passports either, consistent only for the last 20 years... beyond 20 years from now, several passports are missing.

To your other question, my parents application is not in the passport stage yet..we haven't received medical requests either...

I don't think they ever cross-check, but they have to follow the rules to obtain all this information in case this information is needed down the road.

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No trees were killed by this post, but a large number of electrons were terribly inconvenienced.
__________________________________
George Malley: Hey, would you, uh, love me the rest of my life?
Lace Pennamin: No. I'm gonna love you for the rest of mine.
__________________________________
None of us knows God until someone introduces us - Life of Pi

^^ very similar to mine but we have all passports, and yes its stamp on stamp - I mean even we ourselves couldn't figure it out but managed too dig in nostalgia

Another question, you said u put " I had provided the detail in a year format (no months and days)."

where did you put year format? I mean what form? is that the past 10 years activity info
coz the travel form is usually asked at the last stage

I had provided the detail in the 5669 form. Previous10 years had dd-mm-yy format. Beyond last 10 years had year format only.

-----------------------------------------------------------------
No trees were killed by this post, but a large number of electrons were terribly inconvenienced.
__________________________________
George Malley: Hey, would you, uh, love me the rest of my life?
Lace Pennamin: No. I'm gonna love you for the rest of mine.
__________________________________
None of us knows God until someone introduces us - Life of Pi