Why multiple BB-BONE-PRU in /lib/firmware?

I want to enable the PRU, so I have BB-BONE-PRU-01 added to my optarg option. It shows up in my cat of SLOTS. I am unclear if this is enabling both PRU, or just one? I noticed there are four BB-BONE-PRU files in /lib/firmware. I assume I should use the 01, but wanted to know if I need to use another one to enable the other PRU?

The overlays differ in pin muxing and whether or not they're using the
rproc interface. And yes, you probably want the 01 overlay.

All of the overlays enable the PRU subsystem, which contains two PRUs.
You control which PRU(s) you are using when you load a program and start
running it.

Thank you so much. That was very helpful. I am slowly getting a basic understanding of how this all fits together.