HSMP starting date

[nsm2010]

Dear Members,

For instance, If I would be unable to show my presence of 1 year and 11 months (letus say short of 3 months) at the end of my initial HSMP entry, then what are the available choices to show my presence of 2 years.
and
from which date I should start counting the 2years;

my arrival date in the UK,
the date of stamping of Visa,
or starting with the effective date of E.C visa (incase of lapsed effective date)

nsm2010