What doen't you understand? They're not perfectly accurate. No estimate is. Thus, any deviance will call into question their accuracy. It does not, however, refute the claim that they're the best source available. Every source that bases it's times on estimates will deviate from whatever the true time may be.
No, we haven't established that.
Yes, it exists.
I've given you links with evidence that it exists. Your lame attempt to argue that it doesn't exist because it doesn't have a website is laughable.
As am I. Just because I didn't mention them, doesn't mean I didn't know they exist or that I didn't know NFLDraftScout received their numbers from them. In the past e-mail exchanges, they've said the same thing (i.e., that their numbers are averages from the two organizations -- or if only one organization provides numbers, then they just post those).
No, they're estimates. They're low and high estimates. For example, I estimate that the lowest 40 Antoine Cason could run is in the 4.38 range. And the highest possible 40 he will run is in the 4.55 range. I think he'll most likely run in the 4.45-4.48 range, but those are my high and low estimates (both are reasonable and vary by .2 seconds).
It depends on what they're asking for. If when National or Blesto is reporting them to the teams and media they say that the 4.58 time best represents his 40 time regardless of injury, then that's bad scouting. If they say that it represents his 40 time due to injury, then that's reasonable scouting.
Of course the Combine will have the most accurate numbers. No one denies that. But for pre-combine estimates, the best source is National Scouting and Blesto.