For the purposes of trying to calculate treasure you have to make a decision one way or another how to explicitly deal with the deck.
The N American rules say to draw a "random" treasure card and that the deck must be shuffled each time before a card is drawn. It also says any Treasure is returned to the deck after each Quest but hazards and wandering monsters are replaced immediately. This greatly increases the odds of negative cards being drawn late into a Quest when there are fewer good cards left randomly distributed among the bad cards. Doing it this way increases the changes of finding very useful items like Healing Potions, etc. but the random element also means the Treasure deck only has a certain
probability of being exhausted of treasure each Quest, importantly, only in quests with rooms equal to or greater than the number of good treasure cards. This also requires Heroes to card count to some extent because if they've drawn all the good cards during a given Quest there's no point searching for treasure anymore until the start of the next Quest.
Anyway, working with probabilities is fine, but not so useful to figure out how much gold Heroes can attain as the probability stacks each Quest. We could calculate this, but it wasn't my idea of fun. I do have my spreadsheet with all of the rooms and pits recorded as well as how the Treasure deck changes with expansions... so it
could be calculated. With the per-Quest probability factored in the plot would look like the one below, except that the early Quests would be better defined and as the Heroes progress the uncertainty in the upper and lower bounds would deviate exceptionally giving a very wide distribution with a "<" shape, with the large majority of parties somewhere right in the middle.
In general we stick with the original rules, but Treasure is one area that we've changed slightly to make it predictable... but this also makes getting some treasures harder. This is also the method factored into the treasure plots above. So here's how we do it:
1. Treasure Deck is shuffled and the card order is set, we don't shuffle again (until condition 5a or 5b).
2. Each time a treasure card is drawn it's drawn from the top of the deck
3. If it's gold it gets recorded and set aside and if it's permanent treasure, like a potion, it goes to the Hero inventory
4. if it's a hazard or wandering monster it is dealt with and gets set aside as well (technically not returned to the deck)
5a. When the last good treasure is drawn from the deck, regardless of how many treasure cards are left, and the end of the Quest the Treasure deck is rebuilt with the hazards, wandering monsters, gold, and consumed potions.
5b. Alternatively, during a quest, if the last card is drawn from the treasure deck then all of the hazards, wandering monsters, gold, and consumed potions are returned and shuffled in immediately to remake the treasure deck.
If a Hero has a potion in their inventory like the Heroic Brew it's not available until it has been consumed and the treasure deck is rebuilt.
So if you don't know where treasure is located in the deck you can at least calculate that with
X cards in the treasure deck, after you've completed
X rooms (assuming your Heroes search every nook and cranny they can) then the treasure deck will be remade and Heroes will have access to all of the gold again.
I don't know this for sure as it would have to be calculated, but I have a sense that rebuilding the Treasure deck after every Quest
and shuffling before each draw still increases the rate of gold accumulation and significantly increases the number of potions the party will have.
~N
Edit I should hasten to add that I could make another plot with Gold values from Quest notes alone (i.e. you find 85 Gold in a room, or you get 200 Gold for completing a Quest), as I have those recorded as well.