Dutch Safety Board chairman Tjibbe Joustra said on Sept. 09 that the metal objects embedded in bodies did not appear to be from the 777 fuselage.
Dutch Safety Board Investigation Comes Forward With Details On What Hit Flight MH17
The Reuters article that I cited says "500 forensic samples taken from the bodies of the victims and luggage...", so I'm pretty sure the population size of the fragments is 500.
Westerbeke said in the Der Spiegel interview that so far there are no results from the analysis of the 25 fragments. This is the 50th day after the foreign objects have become public knowledge. Investigators have probably known since late July. After all this time they're not sure if the samples are from a BUK, an R-60, or something else. Hence Westerbeke can't rule out fire from a fighter aircraft.
Meanwhile for all we know 475 other objects wait to be carefully analyzed. This process is painfully slow.