After a bit of discussion, this is how we plan to proceed. The initial question you posed shows there’s a bit of uncertainty on how to resolve card effects that seem to target cards that can end up back in your deck. There’s a few ways this can happen, even beyond HLF, but they seem to revolve around the initial state of “your deck is empty, and your discard is going to be shuffled back into your deck, but now you need to resolve an ability, with respect to a card(s) that’s now in your deck.”
The resolution of this, will include a new entry for the Rules Compendium, regarding “Decks, Discard Pile, and Boot-Hill” expanding on what’s currently included in the rulebook for section 2.2.
To be included:
A player’s discard pile and boot hill are public knowledge, meaning a player can check or reference against the stats (Value, Bullets, Bullet Type, Influence, Control Points, Ghost Rock cost, Upkeep, Card Type, Faction affiliation or Drifter status) or keywords of a card in their or their opponent’s Discard Pile or Boot Hill.
However, a player’s deck is not public knowledge. Once a card enters a player’s deck, the stats (listed above) or keywords of any card there cannot be checked or reference against by another card ability, unless that card ability instructs to ‘search your deck’ for a card meeting some criterion.
To your questions above:
Q. When does a player resolving Hot Lead Flyin’ determine the value of “each dude your discarded or aced”
A. We take the answer from the Rules Compendium here (pg. 11 under Step 5 of Shootouts): The loser of the round first chooses all their dudes that will become casualties and what will happen to them. After nominating all their casualties, each casualty is resolved one at a time. Reactions to the loser taking casualties (Takin’ Ya With me, Hot Lead Flyin’) are played after the loser finishes.
Q. When that time comes, how does a player determine what those values are?
A. Check against the printed value of the dudes you discarded or aced, that are now in your Discard Pile or Boot Hill. However if some (or all) of those dudes in your discard pile somehow got shuffled into your deck from a card ability (The pull of HLF for example), those dudes now in your deck are ineligible targets for you to compare the pull value from HLF to their values, since you cannot freely check the card-values of cards in your deck. However, if you have any casualties that resulted in dudes that were aced, and are now in your Boot Hill, or casualty dudes that are in your Discard Pile, check the pull value against them.
Hopefully this clarifies, thank you for your patience while we’ve been deliberating this. If there’s any follow up questions, please feel free to post a new thread with the question.