Good questions! And disturbing reports. If these allegations are true it will likely deal a death blow to the IPCC's credibility, and justly so. IF they are true.
The change from "entirely" to "mainly" does not bother me, barring any evidence of deliberate lies. It's quite possible that whoever wrote the report changed it after learning that it was inaccurate. The change coming before anyone else found out about these other reports leans in that direction at least, barring any other evidence.
But the idea of relying on unsubstantiated reports from non-professional witnesses and anecdotal evidence flies in the face of the scientific method, and these allegations must be investigated fully and quickly.
Even if the allegations are true, I still don't think this is a back-breaker for Global Warming, but perhaps it will make governments around the world pull back on stupid and probably ineffective legislation about it.