Also not asked, but here's my thought.
I don't agree with a blanket statement that the head coach is culpable for everything that happens within a program. There are plenty of areas where wrongdoing can occur that a head coach can plausibly say not only that they didn't know, but that there was no way they "should have known", which is what this concept is stating. It's saying the head coach ALWAYS "should have known" what's going on everywhere.
However, I think in this case, it's something where the head coach "should have known" what Stalions was doing.
Stipulating that what we believe we know (Stalions was working with the OC/DC on the sideline interpreting opponent signs and communicating that to the coordinator before plays) is accurate, it immediately raises a ton of red flags that a coach should be trying to understand how Stalions acquired that knowledge. This is one of those areas where "if it sounds too good to be true, it probably is" comes to mind. I would think that nearly any plausible explanation other than what he was actually doing of how Stalions was able to decipher opponent signal systems would immediately raise the question of "if this dude can do it via legitimate means, wouldn't EVERY team be doing the same?" After all, Stalions doesn't seem to me to have the resume of being so ridiculously smart that he's got a unicorn superpower that nobody else could replicate.
To me, it's the sort of thing where some skeezy guy approaches you in a van and has high-end speakers he's selling for $100/pair. You know those speakers retail for $500 ea. You can just accept that he's got extra inventory he's looking to unload for cheap, or you can be the adult and realize those speakers are either stolen or counterfeit. A dishonest man buys those speakers and tells himself "wow, what a great deal I just got!" An honest man walks away.
To me, this is a situation where a head coach should have known that this was too good to be true w/o breaking any rules.
You've had really good takes on this topic to be honest. I think there's only 1 of 3 realities in this situation:
1) Stallions came to harbaugh or parts of the coaching staff a couple years ago, outlined everything he wanted to do, got full support. Program helped setup the cover. When this came about, they distanced themselves immediately and he will be the scapegoat as they try to avoid the penalties. They're all guilty and crossed the line.
2) Stallions came to the staff and said he's a master decoder of signs. He claims with technology and broadcasts nowadays, he found a way to watch all the videos, analyze signs and provide an edge no one else has. They have no idea he is going or paying someone to be the one recording everything and they thought this kid just found an edge no one else had every thought of because of his Navy background.
3) They not sure exactly how Stallions does it, they know something is being down they probably don't want to know about, so they don't dig in further because after they looked into it, they felt it was somewhat of a gray area anyways. No serious consideration of future events believing that so many programs are attempting to steal signs, so why would they be singled out, even though there was some red flags, which is why they didn't want to know more.
Could be more options than that, but for me those are the most likely and I think 1 deserves the harshest penalty. 3 still deserves penalty.. Will there be any proof that gives us confidence in where it was? Not likely.. Will be interesting to see how it plays out, but I think the only way your description doesn't line up is if it's #2. It's possible, but I have no idea what's most likely at this point.