Entry stamp missing, onus on applicant to prove

Hi all
I have just noticed that there is no entry stamp on my passport for entry to the UK in 2004. I was out for 28 days , I have got arrival and departure
stamp on my passport stamped by Indian Immigration Authority.
Will that be enough to prove that I was out for 28 days or do I need any other documents.
I have read somewhere in this forum that UKBA has told an applicant that he should send additional documents to prove that he returned to the UK.
When applicant mentioned about having entry/exit stamps from destination country ,he was told that he could have gone to any other country.
My SAR disclosure does not have exit/entry informations but I found my attendance letter from the college I attended between September 2003 to September 2004 which is 80%.
Should I send that?
Apart from that I have not got any documents which can suggest my
I am looking for an advice as I am thinking of sending my application within this week.
Regards
Laxman

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