When you put aside the Treasure Deck (as you're meant to do in 2nd EU rules for the Trial only) then a search for treasure has two outcomes: 1) nothing. 2) whatever the note says.
That struck me as pretty straightforward, and again we're talking about a one-off, "special rules for this quest" kind of thing. The Japanese edition has three stages of magic development within the early stages of its campaign as well. Very cool stuff.
The problem with introducing later rule clarifications in supplemental releases continues to this day, which is that you then are asking the GM to gather together all these notes and plan things out and you're asking the designers to maintain this jury rigged structure where new additions have to account for (but also change) previous installments. Instead I would just treat each expansion as its own thing and not apply note rules from one quest to the next unless the same book instructs me to do so. The coolness of whatever my inspiration is could lead me to take something invented in 2023 and project it into a quest from 1989 (or change a modern rule in favor of something invented thirty years ago in a secondary work) but that's every GMs prerogative.
So now you have people wondering how balanced the game system quests will be if the Elf is using the "Elf Spells" or how the Druid and other heroes will fair in those adventures. The good thing of course is that Zargon already decides whether to allow these new rules into other spaces where they weren't originally intended and he gets to decide how they work (if they work at all). The Companion App, not exactly the debate ender when it comes to rules as it follows them imperfectly, already does this to a degree, but your own mileage may vary (and enough is left to the honor system that an individual group has plenty of wiggle room... key example, Sir Ragnar is not allowed to attack, but what if you decide that by handing him a weapon he can? using the App you can still arrange for combat between him and monsters!).
The official answer to the OP's question is that no official clarification is required as these chests are no located in corridors they are located in rooms, that just look like they are corridors. No issue. I was just expressing my dissatisfaction with that approach from a hero player POV, rather than an EWP, as if it looks like a corridor, why would I ever decide to search for treasure when I know that you can only do that in a room.
Rather than concluding the Quest is in error in this case and needs to be rewritten, possibly with a revision to all the searching rules (be my guest), I'd say that the official answer is pretty plain and simple: that corridor is actually a room and functions like one. And I don't even need to go on X or discord and ask for a direct quote from AH to know that.
Zargon's task is very simple:
(points at "corridor")
"this is actually a room"
He is the one who clarifies the rule, as the game is in progress, as he always does. The game doesn't grind to a halt while everyone jumps on social media looking for answers. It doesn't get tossed into the trash because it's "broken." At least it wouldn't have to, but some are too quick to lay aside Zargon's role in favor of appeals to authority and popularity. I for one wouldn't be too happy if my group's game time were constantly being interrupted by such "look ups." When we return to the table next week I may have some introductory note "I did some more research and actually I think we should try playing it this way now..." and that's that.
Speaking of issues.. an unmarked treasure chest IS an error (we can prove this by reference to previous editions where it's clear the note was not transferred, even without looking at drafts), but as many have noted, it's easily solved by simply using the basic rules. No treasure note means you draw a card. AH even admitted this (before they went ahead and corrected all the unmarked chests in MOTM). There was already a work around before any of these designers spoke up, but those who wish to hold their breath until an "official clarification" comes through, they now have their answer.