When they found pieces they believed to be pieces of the samothrace in 2013, how did they determine for sure that they indeed belonged to the sculpture?

The event that happened to this sculpture is that it is much plainer on this side, as the artist must have thought it was not worthwhile expending so much effort on a side rarely seen by onlookers. The back of the statue is quite plain, for the same reason. A number of fragments from the missing parts of the statue are very helpful clues in recreating the monument.