Hmm. Well, neither of you quite answered my question. What I was asking, simply, was: do you believe that anyone senior to you is "sempai" and anyone junior to you is "kohai"?
I am not sure of the literal definition. However, based on my understanding and definition of sempai/kohai, no.
I did actually think I answered the question. Answer (see post #24). There is more involved in the relationship than simply seniority. There is an obligation, acceptance, service, and responsibility that go along with being a senior.
In my old karate dojo, we formally (or informally) would form a sempai/kohai relationship. Sempai was responsible for meeting with kohai outside of normal practice, before class, after class, and also working with them during class to ensure that they were "on track" and doing fine. Sempai had an obligation to ensure that kohai developed and progressed.
I think the same is true, if not formally, in spirit. There is much more than simply seniority.