(I asked you to quantify what you meant by "good" because I was suspecting you were treating a probability of, say, 30% as "good", and we were getting our terms crossed. Obviously not.)

I'd say p>0.75 that the thing it is meant to communicate is that the hero was compromised by Riddle, like Quirrell was in canon.

Whereas I'd put that at roughly p=0.25.

I mean, sure, it might be trying to communicate that, but, I've got:

"Reader! She's about to undercover the Defense Professor is Voldemort!" as a message intended to be sent to the reader but not the characters at about p=0.25.

"The heroic Slytherin discovered something about Riddle in Albania in 1945, and spent his time trying to follow up on it. When Voldemort came back openly to Britain, so did he. What the hero learned in 1945, or in the years between 1945-1970, is going to be important to Harry's defeat of Voldemort, and here's the hint that keeps it from coming entirely out of the blue" (or variations of the theme) as about p=0.15

"The 'heroic' Slytherin died in 1945 in a confrontation with Riddle/Voldemort. In 1970, an ambitious person unconnected to Voldemort then tried to exploit the Voldemort's rise as a chance to make himself leader of Britain under the dead man's name, and died or quit in 1973. Voldemort then found it useful to try the same con as a backup for Quirrel." at roughly p=0.15

And, "Eilizer is planning to do something else with it, that I haven't thought of" at about p=0.2