There was definitely an issue with the Garchomp code. There was a rash of posters on multiple forums who had serious problems after applying it. Either the game wasn't recognized by either Powersaves or 3DS or it would constantly crash after a short period of time. Once these issues started to surface, the code was taken down. It was some time before it was returned to the line up. It was also at that time that rollout of codes essentially froze for about a week (I'm assuming to triple check new planned codes.)
Also, it's impossible to activate a code before the powersaves tab gets it's red check mark. That check mark doesn't appear until it has downloaded the data needed to display what is available for that game. Both tabs become live at the same time. If you don't believe me, click on the cheat tab before the powersaves tab gets its exclamation mark. It will say something along the lines that it is checking with the server (I can't remember the exact wording.)
Now before everybody panics, since the original event Garchomp code was rolled back, the reports of bricks have dramatically decreased. I have only seen just a few reports and let's face it, you will find bad carts out there if you look hard enough (I'm not implying that the people who have posted their post Garchomp bricks are liars.) The reason I said what I did about not using it on my primary cart is mainly due to the fact that I have 2 carts, and I figure why tempt fate especially for an event/item that I can just trade over to myself after I apply the edit?
First of all, until Datel removed the Garchomp code (in fact, until 1-2 days after they removed it), the tabs loaded before the cart OPs were downloaded which confused people and led to cart/save corruption.
Please, inform yourself before randomly speaking out loud.
The only reasons why those reports have decreased are:
1) The tabs don't load until the OPs are downloaded now.
2) People is no longer in a rush to get all the event mons before they remove them. (You cann pretty easily damage your cart's contacts by inserting it too hard on the powersaves dongle).
3) Powersaves and cart bricking has become mainstream so it does not have as much impact as it had when it was new and no one expected it to happen.