hinayana was originally used for non-buddhist schools, which aimed at enlightenment such as the Jains, or some Buddhist schools whose existence were the result of Schism, and I think it would be fair to say the middle vheicle could be Arahant aimed schools and greater Vihicle may of been Boddhisattva ideal aimed, or vice versa depending on who was using the term, or hinayana may also of been used for those aiming at some point on the stream lower than Arahant but not the Boddhisatva path.
the 18 or so Schools weren't all due to schisms (the newer school or branch advocating something which is not dhammavinaya would be a schism) but rather a different philosophic emphasis or way to explain something which is a valid and suits some people.
only the Sthaviravada Vinaya liniages remain, the tibetan schools being part of the Sarvastivada recession and china, Taiwan, japan etc being the Dharmaguptaka recession which is the same brach as the theravadan = Vibhajjavāda
if we look at theravada, Mahayana & Vajrayana today, within each group there are sometimes many different nuances in teaching, but none are actually considdered not buddhist, or schismatic groups with the exception of one Tibetan group (NKT) and a Mahayana group or theravadin group but don't remember the name, I don't think there are any groups which could be called propperly any more schism groups and possibly some of the mix and match groups about could bt that is a seperate thing mostly outside of the vinaya recessions so couldn't acctually be classed as such propperly at least I don't think.
I know one monk dissagrees with me on some of these points (outside of this group) and some of this has been peiced to gether from different sources from seperate inquiries but I havn't seen heard etc anything which is verified from more than one persons point of view or source which has convinced me that I am wrong, so if anyone knows of anything which proves anything wrong please let me know! I do love being wrong about this sort of stuff
(bounties will be given depending on how wrong you proove me