[kps]

Tilde exists in ASCII because of its use as an accent. (In 1967 the non-diacritic interpretation was an overline.) The use in programming languages, and lowering to fit other mathematical operators, came later.

There was never any requirement that ‘n BS ~’ have the same appearance as ‘n’ overprinted with ‘~’, although terminals capable of making the distinction didn't appear until the 70s.

Precomposed characters aren't relevant to illustrating composition mechanisms.