You'll notice that the outdoor NID houses 2 circuits, but has 4 jack/plug/terminal sets.

There are 2 sets for each circuit. The top one is wired RJ-48C, using 1&2 and 4&5. The bottom one is wired RJ-48S, using 1&2 and 7&8.

An inside mount 2-slot NID has a slide switch inside to change the jack wiring.