3DS owners who picked up the device before Nintendo slashed the price were given a special invitation to its Ambassador Program. The program would reward these early adopters with 20 free downloadable games before the end of 2011. All you had to do was turn on your 3DS and sign into the online eShop by 11 August.
However, there was no way of checking if you had been admitted into the Ambassador Program, but now Nintendo has made it possible for you to check if you will be receiving those 20 free downloadable games.
Nintendo has provided a serial number checker on their support site and you can check your status.
For the lazy ones among you, here's the link for the support site.
Source: Digital Trends