I Can't Figure Out the Discrepancy

If, as reported, in Gaza

The number of internally displaced persons (IDPs) has declined, but at least 335,000 people still remain in emergency shelters or with host families. 

and 

Alternative housing will be needed for the approximately 100,000 people whose homes have been destroyed or severely damaged

why isn't the real number of IDPs 235,000?

What is the reason for the discrepancy?

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