NEW HACKS SAVE BACK UP PROBLEMS AND FIX.
When I warned everyone to make plenty of back ups, I’d mistakenly believed they would work the same as the previous hacks. They do not.
Due to the dump and inject tools now being with the game closed, all of them are subject to the time and date check that occurs when the game is loaded. If the time and date of the save do not match the time and date that the game was last saved, the game will state that the data is corrupted and force you to erase your save file. Meaning that all back-up files will not be immediately playable if you have played the game since making the file.
Thankfully, a method to ensure the date and time stamp match has been found here: https://www.reddit.com/r/AnimalCrossing/comments/3j8tbw/fixed_cannot_use_save_data_because_it_was_not_the/
This allows you to load any save file you own, (/other peoples if you choose to send them to someone), whenever you like. But you will need to do some basic hex editing each time. Basically you need to copy the most recent time stamp from the hex file and paste it over the time stamp of the town file you want to inject. Without doing this the game will try to corrupt your saves, but so long as the first 8 values in the hex match the values assigned the last time the game saved it will allow you to load any town you want.
This is a rather long winded method. But if all you want to do is return to a previous back up, you only need to take the most recent time stamp and put it on the back up file. If you have corrupted a save file and require loading a back up to get your town back, you will always need to follow all the steps and create a new town to generate a new timestamp.