If the transistor is a Motorola branded one, an explanation I have seen is that it is the HFE grouping.
And the reason for the grouping was to have similar/matched HFE when used in parallel such as in power supplies.
How accurate that is, I don't know, but the only explanation I have seen for the -2
Some data
https://alltransistors.com/transisto...ransistor=2779