User blog comment:Pellucidar12/Attempt at a FGH related notation/@comment-29915175-20170416151157/@comment-1605058-20170416164119

They were, but they were defined in many different ways and none of them is prefered over the others. Only up to \(\varepsilon_0\) we have a well-established set of fundamental sequences via Cantor normal form. Anything beyond and you are generally required to explain what FSes you take.