Yeah. The only thing I think (but may be mistaken) that is missing from that strategy, is that it does not mention the need for keeping multiple 'versions' of the same file. Even for files you do not modify yourself, like static PDF files.
For example, if pdf file 'A' gets corrupted, it will be considered 'modified' as far as the computer can tell. If this is the 'original' copy, then that corrupt copy will get backed-up (overwritten) on all your other backup copies. You need to keep an 'x' amount of 'previous' (supposedly uncorrupted)'versions' of the same document to account for that. So that when your 'original copy' goes corrupt - and all of the backup copies of that corrupted file - you have a backup that lets you go 'back' to the 'previous version' that was still good and not corrupted.