I just found a big error in a Knowledge Graph snippet on a Google search. The snippet that was highlighted contained inaccurate information that perpetuates an old myth. In fact it sited an authoritative source for the statistics, but that source has vastly different statistics posted online. (The first organic search result had incorrect data, too. That was probably the first organic result because it is a well-known magazine.)
I used the feedback link that was under the snippet to report that it was inaccurate, but I can't help wondering if that feedback ever gets read.
Seeing things like this is sad. While readers of this forum aren't likely to blindly trust anything they see Google highlight, the average searcher is likely to trust a Google Knowledge Graph snippet - and it's the first thing or the first thing that's not an ad that searchers see.