IMO, both the feel of the books and the Atlas roster of titles, and the Atlas staff (kirby/ditko as mentioned) changed significantly in Jan 1959. All of the "first pre hero" (as I define it) books mentioned above are Jan 59 dated, plus or minus a week or two.
Books prior to that I think of as "post-code" rather than "pre hero". It more or less boils down to the maneely/everett vs kirby/ditko eras, though there is more to it than that IMO.
Sad story though it is, I think Joe Maneely getting hit by a bus in mid 58 must have been a terrific shake up to the Atlas office and the Atlas product. I have to guess that was one of the unintended reasons for the change in direction. As a company they lost their most profilic employee in mid 58 and then three or four months later in fall 58 they are putting out these Jan 59 dated books...
I hear Joe Maneely was pushed!
Oh and if it doesn't have Kirby and Ditko doing the majority of the art, its not the prehero books that I'm interested in.