Big credit to all you anons who were hammering the [zero] posts all day yesterday.
I was so busy with my spiderweb map post that I would almost certainly have missed it had it not been spammed, I didn't really read it until much later in the day when you guys were taking HEAVY shilling flak in response (what made me give pause to it).
I spent some time trying to verify the marker, which led me down a train of thought that ended in this discovery. This has opened several more doors, so I anticipate more findings to follow soon, hopefully.
Thank you all for your help.