Tentative “historical” feelings:
A) Keyhoe obviously got some accurate information via leak or whatever, early. He changed some things to protect sources (& probably his trust-worthiness re: his pipelines). But, it’s inaccurate in too many ways. (Keyhoe must play loose to dramatize).
B) Fortunately there’s a lot of solid stuff in Blue Book.
C) Most of that seems to cohere pretty well with the UFO Investigator stuff (a re-interview in 1970).
D) An honest historian, however, wouldn’t know what to make out of Bethune’s claims in the ’98 interview (without more corroborative info than I have – people who’ve studied this case doubtless have more, & so have better ground to judge on). _ _ _ _ _
Re: your question (I think) about radar.
¿ the case does not appear in the Shough RADCAT (augmented by Aldrich&Sparks), so my assumption is that there’s no hint of this in Blue Book.
¿¿ note at the very bottom of the Investigator story Bethune claims to have heard that they tracked it.
According to Corliss’ Lightening, Auroras, Nocturnal Lights, and related Luminous Phenomena, you can get “Auroral meteors” – patches of auroral light which moves, and the North Atlantic can give you some strange auroral effects. But, although “defined”, such patches seem “nebulous” (i.e. they have a fuzziness about their substance) and tend to elongate “in flight”. Whether the ’51 encounter can be crammed into these characteristics seems doubtful.
Plus: no one’s explained these h either.