On or about July 30, 2015, the initial news could have been worded like: "debris appears to have come from a Boeing 777". As the story evolved, additional details emerged such as the wreckage being part of a 777 flaperon, before being decisively announced.

My question is: what was the forensic/investigative process which would have produced the initial speculative-sounding announcement associating the debris to a 777, before ultimately becoming the more definitive statement?

To put it another way: what steps had investigators taken up to the point of each announcement, and how was the debris recognized very early on as part of a 777 without actually being confirmed as such? Is it investigator experience? If initial identification was made by part numbers, why would there have been any doubt in the announcement?