There are different ways that the triennial cycle is read.

Ancient triennial cycle. The Torah is divided into 54 parashot in the annual cycle. ... As late as 1170 Benjamin of Tudela mentioned Egyptian congregations that took three years to read the Torah. In 1517, Daniel Bomberg (a Christian) published the first Bible with rabbinic commentary, divided into 154 sedarim.

Triennial cycle - Wikipedia
https://en.wikipedia.org/wiki/Triennial_cycle