The 19 years I'm referring to are 1993 to 2012 , the date of the issue ,not present day 
Did you miss the 1st line? " The current scientific consensus places the worldwide polar bear population between 20,000 and 25,000 animals." is for 2012
Stirling estimated bears at over 20000 in 1990 , in 2012 it's 20000 to 25000 , according to canadian geographic.
In 2015 it is about 26000 ( 20000 to 32000) see: Global polar bear population size is about 26,000 (20,000-32,000), despite PBSG waffling ,( includes links)
@ polarbearscience.com/2015/05/31/global-polar-bear-population-size-is-about-26000-20000-32000-despite-pbsg-waffling/
Hopes this helps Cletus.