So which one is it? Was Jesus telling Peter the rooster was going to crow once, or twice? Does it matter?
Well, yes it does matter. You don’t want to give someone a “free pass” to say there’s a discrepancy between the Gospels, and therefore there is an error in the Bible. There should be at least an attempt to see why this apparent discrepancy might exist.
However, first and foremost we need to see if it’s really even different. Conclusions are no better than the assumptions upon which they’re based. So, we really cannot just assume the verses disagree without verifying it.