So. The claim.
"3DS games are dying!"
Is it true? Yes, but there's an important thing that needs to be highlighted. It's preventable and sometimes fixable. Genuinely, there is not a reason to panic, but there is a reason to know about this, so that you can take good steps to keep your data safe.
This page is to outline those steps. We'll start with verifying cartridges to keep them in good health, move on to what to do if they're not, and then how to back up data so you don't lose anything even if you encounter corruption later.
2. Download this version of godmode9, it comes with an additional cartridge fixing tool that we may be using later.
3. Get out all of your cartridges, and boot into godmode9. (Hold start while booting up your 3DS.)
4. Insert your first cartridge in the 3DS, and then choose "GAMECART" in the godmode9 menu.
5. Select the file that ends in .3ds (NOT .trim.3ds), choose NCSD image options, and then choose verify.
6a. If verification succeeded, congrats! The cartridge is safe, but you should run this verification check on it every once in a while. (I'd say no more than once a year.) This keeps it in good shape. Move on to the next cartridge.
6b. If verification failed, then we need to move on to repair. I'd recommend finishing checking all your cartridges before repairing any of them, as this takes much longer.
1. Get back to the NCSD image options in godmode9 for the corrupted cartridge.
2. Choose "fix cartridge corruption" and let it run. This can take a while, so make sure your 3DS has a good amount of battery, and remember you can close the screens up and it will still run.
3. When it's finished, you want to go back to NCSD image options and run verification again. If it succeeds, the cartridge is fixed. If it doesn't, continue on to step 4.
4. Go back to the "fix cartridge corruption" option, but hold down the Y button while you select it. This will output a log of what it's doing to your /gm9/out folder on your SD card. Let the fixer run again, and run verification afterwards. (If verification succeeds at any point of this, you're done!)
5. Look at the log. Mark down somewhere how long the list was, and then run the fixer again while holding Y to get another log. You're hoping for a shorter list each time. If it keeps getting shorter, keep running it!
6. If it doesn't get shorter, then those parts probably cannot be fixed. But, for the cartridges that aren't damaged, or that you managed to fix, I'd recommend backing them up.
1. Get back into godmode9 by holding start while booting up your 3DS.
2. Go back to the GAMECART menu, but now select the .trim.3ds file and select "copy to /gm9/out".
3. Unless you have a huge SD card, you should probably move the resulting .3ds file to a computer before dumping another. Repeat until all your healthy cartridges are dumped. Now, if something happens, you have these backups, so keep them somewhere safe.
1. Get Checkpoint on your 3DS. Here's a link to download it, but you can also download it via Universal DB/Universal Updater on your 3DS.
2. Navigate to the game you want to back up the save for. Cartridges can take a second to show up!
3. Choose to back up the save, and name it if you'd like.
4. Some games save important data in the "extra data" section of the 3DS!! So, press the X button to switch to extdata, and then back up any data there as well.
5. Repeat until all your saves are backed up. You can then find them in /3ds/checkpoint/saves for saves, and /3ds/checkpoint/extdata for extra data.
6. Move these backups to a computer, and keep them somewhere safe!
I'm not the biggest expert on this, so here's my simple understanding of it, the type of chip used in the cartridges can corrupt data if it's just not doing anything for a while. This is why it's good to occasionally verify the game, as it makes the chip do something.
"Does this also happen to DS games?"
No! They use a different type of chip that doesn't have this issue. You do not need to verify them to keep them working. However, this could be an issue in the future with Switch games, which use the same type of chip.
"How often should I verify my games?"
I would say once a year at the most frequent.
"Are certain games more likely to have issues?"
It seems so. Notably the Generation 6 Pokemon titles (X, Y, Omega Ruby, Alpha Sapphire), Super Smash Bros, and Fire Emblem Echoes seem to be the ones most often causing problems for folks.
"My cartridge failed verification, but it still boots up fine and I can play it."
This can happen if there's not a lot of corrupted data! It's possible you might run into a problem where one specific thing causes the game to crash later, so I'd make sure to back up your save file so you can move that to a fresh download, if that becomes an issue.
"How prevelant of an issue is this?"
It's hard to say. Anecdotally, out of my collection of 28 physical games, 3 were experiencing cartridge corruption. One was so bad that the game couldn't boot, and two could boot but had small amounts of corrupted data. The cartridge fixer fixed some but not all of the corruption on each of them. (Notably, the games were Fire Emblem Echoes, Pokemon Alpha Sapphire, and Megaman Legacy Collection. So, two of them were games that are noted to be more of a problem.) I hadn't played most of my physical 3DS library for many years at that point, and the majority of it had no corruption.
I would say, don't worry too much about it for most of your games, just try to keep on top of verifying them occasionally if you want to make sure they stay in good shape. Or, at least back up the data so you don't lose anything.
And maybe be a bit wary about buying problem games second hand, especially if they're sealed and you actually want them to function.