My initial reaction was to address this post to JMA; but upon reflection, I am simply going to followup Jon Custis' posts. So, we should address the material facts regarding, and who was involved in, the so-called "intelligence failure" (no POWs); and, more importantly, at what level, should we analyze the end goal of the mission.

In considering those questions, two online sources stand out for factual validation and reasoned policy analysis (fn 1):

Amidon, Mark. "Groupthink, Politics, and the Decision to Attempt the Son Tay Rescue". Parameters, Journal of the US Army War College 2005 (Winter) [cited as Amidon].

Mitchell, Major John, USMC (1997). "The Son Tay Raid: A Study in Presidential Policy". e-History: Vietnam War. The Ohio State University [cited as Mitchell]

1. Events of 19-20 November (the Material Facts)

Amidon's summary (pp.5-6 pdf) is the shorter of the two:

On 19 November, after the President approved the mission and one day before actual launch, word reached General Blackburn of the North Vietnamese HUMINT source who reported “no prisoners at Son Tay.” This HUMINT report triggered a massive reanalysis of available information and demands for an updated intelligence estimate.

For the next 12 hours, General Blackburn, DIA Director Lieutenant General Donald Bennett, Admiral Moorer, and Secretary Laird struggled with the significance of this news and what impact it should have on the mission. General Blackburn was certain that the mission should proceed; yet his confidence wavered as he expressed great frustration with the quality of the intelligence analysis. “One minute they were ‘sure’ the prisoners were gone, the next they were ‘suspicious’ that POWs had been moved back into Son Tay.”[31] General Bennett appeared before Admiral Moorer on the morning of 20 November with two stacks of “evidence,” one saying “they’ve moved,” and an equally large one saying “they’re still there.”[32] Despite this muddled intelligence picture, General Bennett eventually recommended that the mission proceed, primarily on the basis of the “95 percent assurance” that the raiders could safely complete their mission.[33] Armed with the concurrence of his three subordinates, Secretary of Defense Laird routinely notified the President that the mission would proceed as planned. The White House concurred with the Pentagon’s intentions. With the raid due to launch in hours, the Administration was not interested in doubts. As Admiral Harry D. Train, at that time the Executive Assistant to Admiral Moorer, later put it, “They didn’t want to know.”[34]

31. Schemmer, p. 180.
32. Vandenbroucke, p. 65.
33. Schemmer, p. 180.
34. Vandenbroucke, p. 66.
Mitchell's section on "Intelligence and the Decision: (page 6 & page 7) goes beyond Amidon (snips from 19-20 Nov):

....
[the meeting of Blackburn, Bennett and Moorer on 19 Nov] Having heard the opinions of both men, Moorer decided to brief Laird the following morning. Hopefully, the additional time would allow for reconsideration and/or confirmation regarding to the new information. If confirmed to be accurate, enough time would be available on the morning of 20 November to brief the NCA and deliver any changes to the raid force prior to their scheduled launch time.

The following morning [20 Nov], Moorer, Bennett, and Blackburn again met to discuss the new developments. As it turned out, Bennett had a change of opinion. He had reconsidered his position based on all the information collected to date on Son Tay. Bennett arrived at the same conclusion Blackburn did on the day before. Therefore, Bennett recommended a 'Go.' That recommendation was enough for Moorer to agree that the mission should be attempted, since he also believed that the POWs were still there. It was good that all three 'confirmed' what they wanted to believe because the raid force mission commander had given the final preparation and execution order to the raid force earlier that morning. It is apparent that Moorer's decision to wait had paid off because anything less than a unified recommendation from his office probably would have led to an abort by the NCA. However, there was still enough time to do just that with another 'Red Rocket' if Nixon or Laird deemed it necessary in light of the Hanoi source information. Therefore, with Bennett at his side, Moorer went to brief Laird on the recent developments.

Laird did not hesitate in agreeing with Moorer's recommendation to proceed despite the new developments. Laird was committed and fully understood Nixon's policy and to what extent the President would go to make his point once diplomatic efforts failed or produced insufficient results on a specific issue. Laird's resolve and conviction over the POW/MIA would be reconfirmed in his eyes because, within an hour of Moorer's departure, Richard Helms arrived to discuss the information obtained from the Hanoi source and also brought additional news concerning the POW issue. The CIA had intercepted recent "traffic" and confirmed that as many as 11 more POWs had died in captivity in addition to those reported on 13 November. Laird knew he must immediately inform the President of these developments. However, exactly what and how he told the President is an issue which is still debatable.
....
Research indicates, and it is the judgment of this author, that the President would not have aborted the mission in light of this information. Whether or not the President was briefed about the Hanoi source information is irrelevant. After all, the final decision to carry out the raid had been made. In other words, there was no political "smoking gun" (any Presidential "wrong doing" associated with the decision to execute or continue) to be found on this specific issue. However, if the Hanoi source information proved to be true, Laird would take all the blame if the mission turned out to be a total failure. Apparently Laird's decision not to brief Nixon would provide Presidential "plausible deniability" in case the mission met with tragic results. Having established Nixon's policy towards ending the war in Vietnam and what part the raid would play in that policy, let us review the leadership, execution, and reaction to the mission in order to understand the complexity and significance of the Son Tay Raid.
Why was the presence or absence of the POWs "irrelevant" to the decisions made at the National Command Authority level ?

cont. in part 2