If dates were to be added to all the documents, some of the puzzles might have to be rebalanced, but I feel like thematically it would make sense to have dates attached to each document. After all, we are supposed to be going through a document archive, and those kinds of archives usually would be quite thorough in making sure dates are attached to important documents. However, this would also allow for an interesting puzzle where you get some documents whose date is either unknown, missing, or damaged. You would have to find out a rough date for the document before you could fully use it, and it could lead to some interesting puzzles.
Since the documents are currently sorted by date, this would mean that the documents without a date would have to be put in a separate section or smth until you enter it's aproxamate date, at which point it could be put in its proper place in the sort order.