http://databank.501st.com/databank/Costuming:TB_Scout_trooper
The 501st visual guide states what requirement is needed for the optional levels. I'm not sure where it is you were looking or saw. Levels are just costuming acheivements within the detachments for folks wanting as close to screen accurate depictions of the costumes used in the films. Not having a level 2 or beyond costume does not make you any more or less of a 501st member, (unless you're a TK still trooping with an FX helmet . . . j/k).