Well, you don't seem to be quoting (since there are no quotation marks), but reporting. Therefore: The number of humanitarian workers in Darfur had been increasing steadily since 2003 and reached a record 17700 in January 2009 (OCHA-Sudan 1/1/2009).
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Peaceblinkfriendif the number of humanitarian workers is still increasing yet the source is not up to date, can I say '...has been increasing...'?Yes, if that is still a known fact. Then you might have to cite both sources.