I have taxonomies called Groupset and Groupset series.
Groupset series has a term reference field to Groupset to create a hierarchy. Having them in separate taxonomies gives the levels separate names, and makes it easier to configure a reference field on parts that only references the series.
Some groupset series can have additional numbers. For example, Shimano 105 R7100 has R7170 for Di2 and R7120 for disc brakes.
So far, I have kept the series taxonomy to the first two digits, and added parts to represent the additional series numbers.
I experimented with creating a groupset series term for R1720: https://www.retrograde.bike/groupsets/shimano-105/shimano-105-r7120
This is nested under R7100 in the taxonomy hierarchy.
One reason to include them is that they can have different release years.
However, moving Di2 and disc to the series means checking for other related attributes.