I had to draw out a bunch of LEDs to convince myself, but I can see the 4-segment display with just 2 common lines; Digit A segment Anodes are connected to Digit B segment cathodes. Digit A common Cathode is connected to Digit B common Anode.
If the Common line is low, B segments are reverse biased, and only A segments can turn when segment Anodes are high.
If the Common line is High, A segments are reverse biased, and only B segments can turn on when segmen Cathodes are low.
Requires 2 arrays for digits, 1s for A = on, 0's for B equal on.
Neat way to save a couple of pins.
Need resistors on the segment pins (not the common) limiting current to each to < 4mA so that common pin only sinks/sources 32mA and even brightness is maintained as segments turn on/off.
Or add totem pole'd NPN & PNP driver for higher currents (NPN pulls low with high input, PNP sources current with low input).