As you get closer to modern times, the chance of accuracy improves because of mass media (particularly news reels or video), living eye-witnesses, massive government record-keeping, the numbers of history and political science Ph.D. candidates looking for research topics for their doctoral theses, improved forensics processing of physical evidence and so forth.
There are (at least) two schools of thought on Pearl Harbor: complete surprise or LIHOP. There's a lot of info on the US having already broken Japanese military codes and therefore knowing about the attack in advance, and letting it happen to finally break the depression in the US by putting people to work building armaments.
There's a lot of info that US-Japanese negotiations (both through conventional diplomatic meetings and via back-channel, secret talks) were in progress up to the days just before the attack, when Japan pulled its diplomats from the US in what some see as recognizing that no further negotiations would produce a non-military solution.
There's also a lot of info out there that FDR and the US political and military leadership were as surprised as anyone and the US chose to declare war on Japan simply because of the audacity and brutality of the attack.
Personally, I don't see how you could keep such a massive naval operation secret in a time when tensions between the two countries were at the boiling point. But we're spoiled by the satellite age. Back then, radar was in its infancy and I suppose it's possible that prop planes with limited ranges or hampered by cloudy weather just couldn't find anything threatening in their search grids.
An interesting note on radar and Pearl Harbor from Wikipedia: "On entry to World War II, the army and navy had working first generation radar units in front line units, and this technology was relied on throughout the war. The army's oscilloscope type SCR-270 radar detected at a range of 132 miles the Japanese planes attacking Pearl Harbor (although this information was not used effectively by the command level)... From a long piece on the history of radar here:
http://en.wikipedia.org/wiki/History_of_radarAnyway, much as I admire and respect FDR, he was a pragmatist and a realist, as well as enormously intelligent. He needed to give the isolationist country a serious jolt to gain their support in the fight against fascism. And it worked: War is declared on Japan 12/8/41; Italy and Germany declare war on the US on 12/11/41. Pearl Harbor turns US isolationists into instant war-crazed zealots, jamming the recruitment offices and signing on the fateful dotted line.
About 407,000 didn't come back alive. Hundreds of thousands more were badly hurt and suffered from these wounds for the rest of their lives (my father being one of them).
In contrast, 5.5 million German military were killed, along with 1.8 million civilians, a combined 7.5 million that represented nearly 11 percent of Germany's total population at the time.
Just googling and rambling now, obviously, so over and out.
wp