I will take a guess teaching logic systems, pluggable boards, into a common socket, all brought out so you can teach logic, and then wire them together with jumpers to make complete demo systems to show how the logic works. Would explain all being 40 pins, and all having common power and ground connections, along with almost all parts being brought out to the edge connector, instead of being connected into more complex logic, except for the LED decoder, which has CMOS inverting buffers to drive them. CD4009, obsolete a really long time, and made by Harris as well, the second source of RCA original CMOS. Normally you would see a CD4049 there, capable of 50mA source or sink, and faster edges, because it has a cascaded inverter and then a big buffer stage, but instead you have the slow single stage pair of inverting gates.