I'm curious about that explanation--in the seats I'm familiar with, initiation (including all the different potential sequencing modes) is done entirely through

I'm curious about that explanation--in the seats I'm familiar with, initiation (including all the different potential sequencing modes) is done entirely through an explosive train to prevent this exact failure mode (loose Cannon plugs cause plenty of other problems though). We're talking about different things. In "forward both, aft self" mode a front-seat-initiated ejection still ejects both seats in the normal sequence, while in "solo" mode it would only eject itself. For obvious reasons, you would never fly with a passenger in "solo" mode.