When you update a document with the 'Replace document' button, all buyers automatically get access to the latest version of the file. You also get the opportunity to send a message to all buyers that the document has been updated and they can find the new document in their downloads.
To give buyers access to the latest version of your file it is important to replace a file and not remove & upload it again (in this case all previous buyers lose access).
With a bundle, the same applies, only here it is important to know that a buyer pays for the documents that are in the bundle at the moment of sale. If documents are added later, these are not visible to the buyer. The buyer will then have to buy the documents separately or purchase the entire bundle again. Files that are later removed from the bundle will still be visible to the buyer. The same applies to the flashcards.