Of the 20% or so in the labor force, less than 10% don't find a job. 10% of 20% is 2%. So of the poor people not in the labor force in 2008, only about 2% could possibly have been poor and unemployed in 2007.
There may be an additional source term of people who were unemployed but not poor in year N-1. But since the number of people in poverty remains roughly stable over time, this source must also be balanced by a sink of people who were poor in year N-1 but not poor in year N. I.e., for every person who becomes unemployed and enters poverty, there must be another person who leaves poverty (the exact balance varies a bit from year to year). Numbers on this are somewhat harder to come by (most surveys don't track the movement of individuals throughout categories).
(Again, rough numbers, these fluctuate a bit from year to year. )
There may be an additional source term of people who were unemployed but not poor in year N-1. But since the number of people in poverty remains roughly stable over time, this source must also be balanced by a sink of people who were poor in year N-1 but not poor in year N. I.e., for every person who becomes unemployed and enters poverty, there must be another person who leaves poverty (the exact balance varies a bit from year to year). Numbers on this are somewhat harder to come by (most surveys don't track the movement of individuals throughout categories).
(Again, rough numbers, these fluctuate a bit from year to year. )