Heh, the "whole range," eh? Nowhere has it been claimed that a guy could possibly maintain consciousness, without passin out due to lack of blood pressure, for the entire time it takes for the brain to utterly die, chemically-speakin. In fact, the medical authorities I have cited explicitly say otherwise. They said "two seconds at most," if I remember rightly. The second cite merely says:
"If that [loss of consciousness] weren't to happen immediately, an individual could in theory remain self-aware for part of the thirteen-second period."
Hint: "Part of" aint the whole, get it?
Are you ready to be really really embarassed? This is why you actually need to track down full articles instead of relying solely on summaries on about.com and wiki.
Here's a longer version of the quote from Ron Wright in Cabinet Magazine.
The evidence for the survival of awareness (as opposed to brain activity) after decapitation remains inconclusive. According to Dr. Ron Wright, a forensic pathologist and former chief medical examiner of Broward County Florida, "After your head is cut off by a guillotine, you have 13 seconds of consciousness (+/- 1 or 2). [...] The 13 seconds is the amount of high energy phosphates that the cytochromes in the brain have to keep going without new oxygen and glucose."4 Naturally, electrochemical activity is no guarantor of conscious thought, although as Wright notes, there are alleged instances of disembodied heads blinking in response to questions, "two for yes and one for no."
https://www.cabinetmagazine.org/issues/10/severed_head.php
Again, I would emphasize that the original source for this quote, the urban legends web page no longer exists, but that explicitly contradicts your intepretation of your "medical authorities." It provides a range, and acknowledges explicitly that there is a difference between electrochemical activity and concious thought while stating the evidence is "inconclusive." Your source also acknowledges that there are reported instances that run counter to the 13-second and instant loss of conciousness hypothesis.
I'm sure you will have some reason why we're absolutely certain, but at this point you're just trolling anyway.