How can I make electrical connections over v-score line?

I am designing a 2 layer PCB with components on both side of it. SMT components are one one side of PCB, but TH (through hole) components are on both sides. I need to understanding something mentioned by the supplier called primary and secondary sides.

While bored recently, I decided to take apart a few old pieces of electronic equipment and attempt to reverse-engineer them. I’ve been doing pretty well, but I’ve come to an IC that I can identify but doesn’t seem to exist on the manufacturer’s website.