Luke chapter 1

Writing to Theophilus, the author clearly states that there are many accounts of  Jesus' life. As I wafe back into biblical scholarship, I noticed once again, that critics seem to think and if it's old it's worthwhile. So if there is a gospel discovered that's as old as the canonical Gospels, it's somehow worthwhile. Yet, at the same time, there aren't any gospels that age that survive. So on the one hand, they want to discount them because they are not close enough to the events, but they also want to discount them, because there are accounts that are later?