Archaeological Material from Syria Seized in Turkey

There are reports that Syria would like details of some 2000 objects seized in Turkey (Shadia Nasralla, "Syrian antiquities chief says Turkey refuses to return looted art", Reuters, December 11, 2015). What is important about this report is the note on the level of seizures:

The 2,000 objects seized in Turkey compare with 6,500 recovered by Syrian authorities from smugglers, 300 seized by Jordanian authorities and 90 returned to Syria from Lebanon since the beginning of the war, according to Abdulkarim.

Earlier in the year BBC reporter Simon Cox reported on some of the material that had been seized in Lebanon ("Are looted antiquities from Syria funding IS?", BBC News February 18, 2015). These reported seizures are likely to be the tip of the iceberg. Where is the other material that has not been intercepted?

Cox was able to identify some material that was appearing in London ("Islamic State: Looting for Terror", BBC File on 4, February 22, 2015).