Some GLO's start with Alpha and go through the Greek alphabet until they hit Omega. Then they start with Alpha Alpha through Alpha Omega, Beta Alpha through Beta Omega, etc.
Others break it down by state, so the first chapter in Massachusetts would be Massachusetts Alpha, the first chapter in Ohio would be Ohio Alpha, etc.
AEPhi did something a little different. They went from Alpha to Omega, then went from Alpha Alpha through Alpha Omega, then Epsilon Alpha through Epsilon Omega, then Phi Alpha through Phi Omega. After that they started over with Beta Alpha. So I'm from the Beta Epsilon chapter, but we were the 101st chapter chartered.
HTH