A specific term was first coined in a preprint but publication took many years. What to cite?
I would try this:


  Miller et al. (2000, p. 13) coined the term "underwater spaghetti knitting" (see also  Miller at al. 2005, p. 8).


Or this:


  This phenomenon became known as "underwater spaghetti knitting" (Miller et al. 2000, p. 13; Miller at al. 2005, p. 8).


Here, Miller et al. 2000 is the preprint and Miller et al. 2005 the final publication.