Why exact date?

[Longman]

CRA refused “STATEMENT OF RESIDENTâ€￾ that I filled and asked the exact date – not only month and year also Date! I am unable to remember the date when I entered Canada. I don’t know how the Date is important. Anyone can help me? Thanks in advance.
By the way, what is definition of “enteringâ€￾ and “leavingâ€￾ Canada? I back and forth several times each year.

Background:
I am Canadian citizen. I have been working in USA since 2000, and back-forth Canada regularly because my family is in Canada. I filed the tax return in 2007 tax year because I also worked for a Canada company. In 2008 and 2009 tax years I did not file tax return because we called the CRA office and the officer said I don’t have to file tax return to Canada. In 2010 tax year, I filed tax return and submit some tax to CRA after subtracting tax to USA. But the CRA replied say: I was “non-residentâ€￾ in 2010 tax year and have to pay more tax to CRA. I indicated my family is in Canada all the year and I should be “Factual Residentâ€￾. They, then, asked me filling a NR74 and NR73 to determine my residency.