If it IS combination of all (or partly) codes from other pieces, then there's my suggestions.
(As with every last puzzles

) there's presumably can be connection with 8291 - so it could be that pieces 8, 2, 9 and 1 - is all we need, perhaps in such direct order or without order, perhaps we have to combine them somehow, to form some word or IDK.
It could also may have an another meaning - perhaps all codes EXCEPT pieces 8, 2, 9 and 1...
I also noted that there's numbers in pieces:
2, 3, 4, every number on the different positions. So I could only suggest that 7 piece will contain either 5 or (more possibly) 1, on the last position, like
It also could be an order... I just really ran out of ideas.
I may only suggest to use any unused keys\phrases from before, like, we still don't know what
:
I CAN HELP YOU KNOW THE DATE
was for...
EDIT:
Perhaps "WHO" will help us to solve this? What is WHO? First letters of words? File type?
"Who will help" - SAVIOR?