Pretty much, yes. There are a multitude of conflicting accounts, and in addition, a rather annoying proliferation of bad arguments in modern scholarship. Having said which, the primary sources are not that bad, all things considered, and it is possible to get a reasonably coherent idea of what probably happened. Since I wrote the book so kindly linked by @Gabriel_L, I haven’t seen any reason to change my main arguments; on the contrary, I’m more confident about it today.
The key is to realize that each of the accounts we have is sectarian, which means that it was composed by a school in order to authorize their own specific point of view. This means that all the accounts are, in some sense, origin stories, which owe as much to mythology as they do to history.
To ward off misunderstanding, by “mythology” I don’t mean “falsehood”, but narratives whose primary purpose is to create a sense of community through emotional connection and transcendence. So history and mythology are not mutually exclusive; rather, they are different aspects of the same thing. They may or may not be true in the sense of things that actually happened; but they are felt to be true in a sense that transcends mere time and space: “things that never were, but always are”. So when we encounter mystical or impossible things in the accounts, we shouldn’t simply reject them, but use them to help understand better the underlying identity and desires of the school.
Anyway, here’s what we can say, so far as is based fairly securely on the original accounts, and is reasonably generally accepted today.
All the accounts agree that the primary doctrinal schism was between the Sthavira and Mahāsaṅghika. These schools subsequently divided into multiple schools, which became known as the “18 schools”. The number 18 is conventional. In fact there are many more schools than this mentioned in the accounts, and of course this changed over time. On the other hand, most of these schools were mere regional variants, and there were only about four or five really significant doctrinal schools.
Here they are, with their most distinctive doctrines:
- Theravāda, incl. Dharmaguptaka, etc — reject all the below
- (Mūla-) Sarvāstivāda — all phenomena exist in the past, present, and future
- Puggalavāda — there is an individual who is reborn, which is not a self
- Mahāsaṅghika — an arahant may have flaws, and Buddhas are better
The first three are descendants of the original Sthaviras. I could expand this with other schools, but it is not clear how many of these were really distinct in doctrinal terms.
Here are the specific points that I argued for in my book:
- The most reliable sources for the Ashokan period are the Ashokan edicts and the Sinhalese Vinaya Commentary, which is preserved in both Pali and Chinese. The Chinese text predates the Pali. (It was, I believe, made from one of the commentaries that Buddhaghosa used as his sources.)
- The earliest and most reliable source for the primary split is the Mahāsaṅghika Sāripūtraparipṛcchā in Chinese translation.
- None of the splits between the schools was a “schism” in the narrow sense as defined in the Vinaya.
- The separation between the groups arose primarily from geographical separation, especially as a result of the missions sent out in Ashoka’s time.
- The Second Council—100 years after the Buddha—records tensions in the community, but these were healed and did not result in schism.
- There was no schism before Ashoka: all reliable records, including the edicts, refer to a unified Sangha.
- The split between the Sthaviras and Mahāsaṅghikas happened some time in the century after Ashoka.
- The fundamental issue was the nature of the arahant.
- This was likely to have stemmed from a specific personal issue: i.e. the very common problem of a guru who was believed to be enlightened, but whose behavior did not meet those standards.
- Nevertheless, all of the sources are careful to avoid describing the split as a schism, which would result in a definite rebirth in hell for the proponent.
- There are few if any records of definitive splits happening between other schools, so it is likely that in most cases they simply drifted apart.
- An important implication of this for the study of the Suttas is that the early texts were separated on the basis of geography long before doctrine. By the time of Ashoka, Buddhists were as far apart as Sri Lanka and Afghanistan. And, as it happens, most of our early texts stem from these far-flung reaches, not the middle country.
- Sectarian differences in the Suttas are of marginal effect. The sects were primarily defined as monastic communities, so the real sectarian documents are the Vinayas.