OK, I changed "bug" to "problem". I could change it to "potential problem" but I felt it got too long. I hear what you say, but if feel that if they know that the tattoo means evil cult the "twist" gets too simple, so the adventure/campaign needs modifications. Or?To use the word "bug" here is misleading. Your players found some clues. Clues that the campaign even adress that they can follow up on later in Outskirts, which the players most likely will get to next. Smart players (they don't have to be that smart really) knows that there is more to this story than whatever information they got during the first session and they should research more about this with caution.