I am going to say this with the utmost respect and hope you don't take it wrong.
If you are going to DIY the process, you NEED to invest time into reading forums. This is the first time in about four years that I have been a member here that I read of someone expecting the I-797 to be the approval notice. It is well known, for us DIYers, that 751s are taking a year at its best.
Second, the name of the stamp is ADIT and it stands for Alien Documentation, Identification and Telecommunication. I am saying this because you literally wrote "add-it" stamp, and no, it is not an add-on to anything.
Again, if you are going to DIY, please please spend some time educating yourself. Otherwise you can make very costly mistakes.