I think it's just a silly scenario that has no reason to ever come up except to justify a lie tag. It could just as easily be "I can get us through this forest," no mention of the past. That line still does everything it needs to do. KIS. Keep It Simple.
But it doesn't work for "I once led a team of miners out of a collapsed mine. I think I can get us through this forest."
All statements the player makes should serve a purpose. And the statements should be designed to fill that purpose. Is the player trying to get another character's trust? Is the character trying to get a character to do something? What do you see being fulfilled by the lie that isn't equally fulfilled by just leaving it open?
Let's look at the scenario. Characters are stuck in the woods. You want to let the player characterize themselves before leading people out. What kind of characterizations are good? Confident? "Let's get out of here!" Experienced? "I know how to get us out." Uncertain? "I don't know, but let us try." Reluctant "Maybe we should wait? What does the group think?" What does the lie about mine collapses serve? To boost morale? "I know how to get us out" does the same thing, true or not. And it doesn't matter if it's true if you never try to call in the lie. The player gets to formulate his own justification behind the statement that may differ from the author's intent.
Maybe you're thinking you'd like to call the lie out. To which I have to ask, why? The vast majority of lies should let the player get away with because it makes them feel they are successful at what they want their character to do, lying. And thus you can treat the lies and truth with the same outcome.
I understand what you mean. That wasn't the best specific example, as I was just trying to point out the way in which such a lie would be presented, and I failed to present a necessary lie.
The idea I'm getting at is, sometimes you need to provide details to further convince people of things. Look at people trying to find a surgeon for a risky surgery. They don't just say "You shouldn't worry, because he's really good at surgery." People often say things like "He's performed over 1,000 successful open-heart surgeries. So you see? You have no need to worry, ^_^"
Just like foreigners fearful of an attacking army might be told "These walls have held off a number of armies greater than than the years of your life thus far."
The point is, you might need to present such info to bolster someone's confidence and alleviate their extreme doubt or fear, and sometimes YOU might trust the person who's doing something, but the other person knows nothing about them, and doesn't know you, either. So, saying "Trust me (a complete stranger), this other complete stranger is totally awesome at this!" isn't gonna cut it."
You're helping some person escape from some dungeon, and they're FREAKING out. They don't know if you're criminals, or what. Maybe if you say "Look, he'll get us past those locks, don't you worry!", the person calms enough to come with you, but dies along the way (because he's still scared into ineffectiveness), or he just doesn't help you nearly as much with the rest of the escape (so, if you care about saving him, you've got to put up with protecting him while he just cowers around in corners, AND the lack of his fighting strength.) So, maybe you say "This guy once singlehandedly broke into the royal palace, stole an ornament from the princess's chamber, then got back out, all in the span of a guard shift change. I've never seen anyone as skilled as him." And now he isn't worried about being trapped in there, so he regains enough composure to ask for a weapon and help you fight your way out. Maybe he lives, and you run into him again down the line (maybe he provides more quest opportunities, or affects other quest circumstances in some way, *shrug*.)
The point is, HOWEVER the speech system is handled, I'd assume that ALL options aren't available to ALL people. So,
1) How do you even know that's taking advantage of your focus on deception progression if it doesn't tell you it's a lie? and...
2) How do you even know whether or not your character simply knows that guy is that good and knows that the past event described actually happened?
The 1st is really more important.
Again, I maybe can't think of the absolute greatest scenario off the top of my head, but if you NEVER have a similar scenario, then what the hell does being a skillful liar accomplish over being a non-skillful liar? No characters will EVER be better at pulling off the believable delivery of a lie than other players?
Do salesmen get people to buy things by saying "Oh, it's really good, and you want it, trust me... I mean, it's just... it's SOOO good. It's a wonderful product!" No, they exaggerate the crap out of everything, at the very least (which is pretty much lying... it's deception), and the less reputable ones lie about things ("Sure, that won't break for like... 5 years!").
I just don't see the benefits of making sure nothing is tagged as a lie while negating ANY even remotely similar scenario, as opposed to making sure lie options (that you're deciding to choose in dialogue in lieu of other options) are clearly marked, and being able to have SOME amount of make-stuff-up-that-the-player-probably-doesn't-know-isn't-made-up-to-affect-people scenarios in the game. *shrug*
I think that IS keeping it simple. "If it has '(lie)', it's a lie. If it doesn't, it's not a lie." Instead of "Wait... he said he knows how valuable that jewel is... *flips through a bunch of lore and history*... is he lying? If he is, is it possible other people KNOW he's lying? Crap, I wanted to play a character who tells the truth. I could've picked another option for that very reason, had I known this one was a lie!"