I know that A Perilous Voyage says your threat cannot be reduced by player card effects. What I'm curious about is does that cancel cards that prevent your threat from being raised in the first place. For instance, a card like Ever Onward that prevents a players threat from being raised after questing unsuccessfully. Thanks in advance.

Reducing your threat has previously been defined, e.g., here : 'In every case where card text says that your threat “cannot be reduced” it means that the actual value on your threat dial cannot go down.'

Something like Ever Onward never causes the value on your threat dial to go down—as you already pointed out, it prevents the value from going up in the first place—so it has no direct relation with the threat reduction prohibition on Perilous Voyage, and thus works normally.

Thanks for the reply! That's what I hoped.