Dear All,
I think it is important to distinguish between the CONFIRMATION number that you received when you entered the lottery online last year, and the SELECTION number you will receive on May 1st if your entry was selected for further processing.
The CONFIRMATION number starts with 2012, and then has a series of coded letters and numbers which probably stand for the date and time you submitted your application. There is no magic as to how many letters or numbers are in your CONFIRMATION number. It is just their particular algorithm for identifying each entry.
If your entry was selected for a chance at a green card on May 1st or afterward, you will find out your SELECTION number. The SELECTION number will start with the year, 2012, then have a two-character code for your region (OC, EU, AS, etc.), then a sequential number which indicates your "place in line" for your region. The lower this sequential number, the better your chances of actually getting an interview.
The SELECTION number is what drives the timing of your interview. You will be referred to a site where there will be "bulletins" issued. Each monthly bulletin will let you know where the "Queue" for your region is at the moment. Again - the lower the number, the sooner you have a chance to be processed.
You may go to the site on May 1st and receive the message I got last year "Your entry has not been selected for further processing." So sad.
Remember, there are only 50,000 green cards. If there are large families in the queue ahead of you, then the green card slots will be used up faster.
Good luck to everyone.