...CGRAM address only 8 (I guest....:> )

You are correct, sir. A person might think to display the first 8 custom characters, then write the next 8 character patterns to CGRAM, and then display the next 8 custom characters. This will not work because the LCD controller continuously references the CGRAM and CGROM during display refresh. Wherever a particular CGRAM character is displayed, all those displayed locations change the instant the character's respective CGRAM locations are changed. That could make for some nifty effects, I suppose.