The cuneiform na sign is a common, multi-use sign, a syllabic for na, and an alphabetic sign used for n, or a; it is common in both the Epic of Gilgamesh over hundreds of years, and the 1350 BC Amarna letters. In the Epic of Gilgamesh it also has sumerogramic (capital letter (majuscule)) usage for NA. An example usage for NA in the Epic is for the spelling of NA.GAD, (also LÚ.NA.GAD, and the plural LÚ.NA.GAD.MEŠ), for Akkadian language "nāqidu","herdsman". The usage for NA in herdsman is only for 3 spellings.
The commonness of cuneiform na, in the top 25 used signs by Buccellati (Buccellati 1979), (2nd highest usage, exceeded by a: a (cuneiform)) is because of usage for the spelling of a-na (Akkadian language "ana") -, the common preposition spelling for English language: to, for, by, of, at, etc.. It is also a component for the Akkadian language preposition: i-na (ina), meaning: in, into, by, etc..