Or there aren't objective standards for what "low, medium, and high confidence" actually mean, thereby allowing one agency to look at the evidence and say it's of low confidence and another to look at the same data and say it's moderate confidence.

Interestingly, the CIA has published a paper on exactly this subject:

Words of Estimative Probability (PDF) https://www.cia.gov/resources/csi/studies-in-intelligence/ar...

Moderate and Low are Words of Analytic Confidence [1]. This has more to do with the quality of the sourcing than a numeric probability number.

https://en.wikipedia.org/wiki/Analytic_confidence

Or they are coming to different conclusions given the same ambiguous/incomplete information. It could simply be disagreement, or just lack of a standard metric here to compare notes easily.

It probably just means the correct aggregate conclusion is “we don’t know, go ask China”.

I read that they did massively increase sharing after 9/11, but there was a reassessment after the Manning leaks. Manning had access to way more information than someone at their level needed for their job, and they concluded this came about from going a bit too far on the post 9/11 sharing and so they dialed it back a bit.

They improved the ability to share info (fusion centers and whatnot), but the desire to do so remains under the auspices of humans.