It was an error because he had to shift Barritt to 13 where he got exposed.
Yes, but there was a forced selection change at 13 due to Joseph's injury.
Of course Slade could have come in at 13 and that may have been a better option.
Lancaster's error was potentially selecting Barritt at 13 over Slade.
Selecting Burgess at 12 after deciding that he preferred Barritt over Slade at 13 wasn't an issue. Burgess went pretty well.