I think concede is perhaps not the word here. Even the most immovable of fundies would say anything outside the Bible is fair game for assassination, and that a lot of subsequent writing about Jesus is just not history.
There are a range of tools we can use to support the reliability of different parts of the Gospels. Things like multiple attestation, criteria of coherence, embarrassment (as the OP) etc. We can also use other tools such as the development of theology (just why did a Jewish sect declare the arrival of the Kingdom of God (KoG) when it plainly hadn't arrived? Why was resurrection, a small and debated aspect of the KoG put smack in the centre of belief?)
As for the events of Matthew 27:51-53.
More puzzles than answers. Did Matthew mean to imply that the risen saints were lurking in the tombs between Jesus' death and resurrection? What happened to them afterwards? How many earthquakes over the three days? Could this have been a way of turbocharging the start of the Early Church by getting some key 'witnesses to miracle' to sign up? Why has Matthew written an account of an event full of imagery as the fulfilment of OT texts, when Jesus' resurrection was the fulfilment?
And most crucially- Why is he risking telling a story that would literally steal Jesus' resurrection thunder?
It's one of these things where you say it's just so bizarre it probably didn't happen, but so much about it is odd that it must have.
There are a range of tools we can use to support the reliability of different parts of the Gospels. Things like multiple attestation, criteria of coherence, embarrassment (as the OP) etc. We can also use other tools such as the development of theology (just why did a Jewish sect declare the arrival of the Kingdom of God (KoG) when it plainly hadn't arrived? Why was resurrection, a small and debated aspect of the KoG put smack in the centre of belief?)
As for the events of Matthew 27:51-53.
More puzzles than answers. Did Matthew mean to imply that the risen saints were lurking in the tombs between Jesus' death and resurrection? What happened to them afterwards? How many earthquakes over the three days? Could this have been a way of turbocharging the start of the Early Church by getting some key 'witnesses to miracle' to sign up? Why has Matthew written an account of an event full of imagery as the fulfilment of OT texts, when Jesus' resurrection was the fulfilment?
And most crucially- Why is he risking telling a story that would literally steal Jesus' resurrection thunder?
It's one of these things where you say it's just so bizarre it probably didn't happen, but so much about it is odd that it must have.