Why studying Long Lance plans was not enough

What if Allied analysts had properly studied the Long Lance plans they received?

They did study them, but wrongly decided Japan could not build the torpedo the plans described.

The captured information did not simply go unread. Analysts studied the plans and understood what they described. Their failure was an intelligence judgment: they concluded that Japan could not actually manufacture the weapon shown on paper. The Long Lance surprise therefore arose from dismissing an adversary's industrial competence rather than from lacking access to the design.