Star Guardian vs Baron

ok so in the S.G video it has the whole squad killing baron nashor right, so in the lore of the rift it says that when the summoners were almost or were finished with the rift they went to go see what to do with nashor but he was gone! so the summoners made a replacement baron. is it possible that the S.G killed baron nashor before or after he left summoner's rift or is it what the S.G are killing is just another replica?