A succinct Soufan Group briefing note, the keypoint IMHO is:
Both the UN and U.S. estimates find that nearly 30,000 people have traveled to Syria; the monthly rate of 1,000 remains unchanged
Link:http://soufangroup.com/tsg-intelbrie...eign-fighters/

Their argument is weakened by no mention of the recent ICSR report and nowt on those who change their mind.