So with your idea, the ICIG is in on it too?
A well-designed hypothetical leak-detection mechanism would include literally everyone in the organization, except maybe the most senior leadership. So even if the ICIG knew of its existence, if the system were designed well, they would have no way of knowing which documents were false.
If the ICIG were aware of the existence of the system, they'd also have to keep it secret, which would mean that even if they suspected Grusch was referring to intentionally false documents, they'd have to handle it as though the documents were genuine and forward it on to Congress just like you're describing, right?
I suspect what will happen is that the intelligence committees will meet with the involved parties in a SCIF. Someone will explain that the documents were intentionally false information. The committees will verify this discreetly. After that, I could see three main approaches for handling the situation:
* The committees make a vague statement that they've investigated the claims and there's actually nothing to worry about after all. They'll have Grusch support that claim, but not discuss specifics.
* Same as previous, but with the inclusion of some sort of excuse for the misunderstanding, like the Project Azorian "mining manganese nodules on the ocean floor".
* They'll decide that the amount of detail Grusch has disclosed publicly is too great to convincingly sweep under the rug, and decide to come clean about the leak-detection mechanism.
If they go with either of the first two, it will fuel decades of conspiracy theories about how the government covered up their secret captured alien spacecraft once again, but that's nothing new.
If I'm right about this kind of mechanism, the people running it might even encourage such things to create a pool of far-fetched lore in the fringes of the public. That way, they could randomly sprinkle in false documents related to those things specifically to catch people likely to leak fringe-related material early in their careers, before they're given access to really sensitive information.
I do absolutely think that Congress should follow the trail and see if there's physical evidence. I'm just saying that I think that what they'll find is that there was never real evidence, just intentionally fake documents and maybe faked artifacts.
Potentially, it could also be a mix of true details, but wrapped in a false backstory. e.g. if an intelligence agency captured a Russian weapon prototype in some underhanded way that would cause a political incident, and wanted to have people reverse-engineer it, they could remove any identifying markings, then let three people examine it separately. Reverse-engineer A would be told "it's from a vehicle of unknown origin that crashed in Colorado". Reverse-engineer B would be told "it's from a North Korean military satellite". Reverse-engineer C would be told "it's from a crash site in Wyoming". All three might be provided with different, faked photo evidence that matched the story as part of their documentation. If any of those stories showed up in counterintelligence records, the intelligence agency would know which engineer couldn't be trusted. Everything else I described for the simpler scenario applies there too.