Well, it's clear from IP(TSF) 69 and 70 that Charlie knows that Faq exists, that Jillian is from it, that its ruler is (was) King Banhammer, that it is (was) located near El-Efbaum, and that Jillian knows that Charlie knows this.
He knew that Faq existed back when it existed the first two times, but that was some unknown number of turns in the distant past. Jillian has been a full-time mercenary for all of recent history, but now suddenly, a few turns after Faq is re-established as a secret weapon against Gobwin Knob Jillian is getting a call from Charlie calling her "Royal Highness." Jillian is clearly wondering how Charlie knows about the new
Another point is that when Charlie talks about his "secrets" being compromised, Jillian assumes that they're "trade secrets" and scoffs at him. But Jillian should know from personal experience that Charlie has some *personal* secrets that he values very highly.
Charlie may value them highly, but they don't seem highly valuable to anyone else. Jillian has no reason to care about Charlie's history in el-Efbaum, no reason to think that sort of secret was exposed, and every reason to think that Charlie is talking about trade secrets because those are the sorts of secrets that might matter.
And while it's true that Jillian doesn't trust Charlie, the time period mark of "when he was her main competition for mercenary work" sure seems like a strange checkpoint over "when she almost croaked his daughter for trying to negotiate with him".
"When he was her main competition for mercenary work" is another way of saying Jillian's entire life up to her refounding Faq. She's saying that she has never
Retconjuration may not be strictly necessary -- certainly it's possible that the "deal" with Charlie involves not just Faq never talking about Charlie, but also forgetting all they knew about Charlie.
Since nothing has been said that explicitly contradicts canon, retconjuration wouldn't be strictly
necessary even if Jillian remembered everything.
But Jack and Wanda's behavior is more consistent with them knowing Charlie's history with Faq yet not being allowed to talk about it, as opposed to actually losing memory.
There is no doubt at all that Jack and Wanda remember. Jack even told Parson all about it in Epilogue 7.