I seem to remember explanations by ktom that went like this, although I don't recall if they concerned NE or other effects.
Well, the explanations of "no memory in the OOP area" are more about why lasting effects on cards in play (like "at the end of the phase, return this card to your hand" or "gains an intrigue icon until the end of the phase") end immediately, duration complete or not, when a card leaves play.
I'm sure you are right, but could you explain to me the difference between this and the situation in which Narrow Escape cannot bring back a duplicate that was discarded that phase, even though at the point Narrow Escape is initiated, it is simply a character card in the discard pile?
There is a certain amount of implicit "it works because it works" reasoning with the situation, but the two situations really aren't all that different.
Compare the Campfire Bard/Sam example with the dupe Jaime/Castellan of the Rock example. We said that when you play the Bard, an "after a character is played" Response opportunity is generated. When Sam's ability initiates, that's when you look to see if said character was a Raven, meeting all of Sam's play restrictions. However with the Jaime/Castellan example, it is in part true that when you go to initiate the Castellan, no new character has entered play, but even more fundamentally, we know that playing a dupe is considered "playing a dupe," not playing a character. So the "after a character is played" Response opportunity was never generated in the first place. Perhaps an easier example is the various Chambers being played as an attachment instead of a location. There is no "after a location was played" Response opportunity created because the card was played as an attachment from the get go.
Narrow Escape effectively combines the "what is the card at the time the effect is initiated?" concept with the "what opportunity was created?" concept. Because the card specifies that the character had to have been killed or discarded from play that phase, the only cards that can be eligible to be returned would be characters that left play. Said another way, only cards that created an "after a character is killed/discarded" Response opportunity meet the first threshold for Narrow Escape. So that's why character cards that left play as something other than character cards do not count; a character was not killed or discarded. The second threshold is that the card itself must be a character card, otherwise, you are not returning a character to play.
Essentially, Narrow Escape looks at each card in your discard and dead pile and asks two questions: #1 - is this a character? (answering "no" is why the Reinforcement events stay put) and #2 - was this character killed or discarded this phase? This is where it looks at a dupe and says that the "character" this individual card represents was not killed or discarded.
The "Characters discarded as dupes do not count as discarding characters" reasoning really is the same as the "Chambers played as an attachment do not count as playing locations" reasoning, just with the card leaving play instead of entering play.