I am 100% positive that Marshall has two 8 ohm parallel pairs of 16 ohm speakers in series for 16 ohms parallel-series. First word is how the 2x12 pairs are wired, last word is how they're wired at the jack. That's why there's two 8 ohm (2x12) jacks for stereo and then both in parallel for 4 ohms.
View attachment 426542
Mesa is similar, but using 8 ohm speakers means two 4 ohm parallel pairs but no 2 ohm all parallel.
View attachment 426539
Bogner and Friedman come one jack, two series pairs in parallel. That's series/parallel. Dave confirmed he wires them up like the Aiken diagram. Shortest runs/least amount of wire, a neat way to do it.
Diezel does it the way I like it, with two series pairs of 8 ohm speakers at 16 each for stereo, then in parallel together for all 4 at 8 ohms. Framus does this as well.
View attachment 426541
Most people prefer series/parallel wiring in a 4x12.