They spawn in regular intervals. For example, the trader at Billy's farm spawns every 21 days, which is 3 weeks. Other traders have different intarvals, like book trader at Riverstone, which appears every 7 weeks.
It's possible you just got unlucky, but there is also a possibility that something broke on your save and they stopped spawning.
Yep I know about their rotation, I think because I skip Billy cutscene with the 3 gang member make them can not spawn since that the only difference in the 1st playthrough. Also is there anywhere I can ask about alchemy system, ending hints, secret hints, inchor container's spawn location detail since they make me play like hours aimlessly which stall the progress for me. Do the game has a wiki? Last night I even spent 30m to try kill the Ghoul just to realise later they have 6000hp not around 2000. Thank you for your time reading this
The game doesn't have a wiki as of yet. I won't be making one any time soon because working on the game and the wiki would slow me down even more. I have nothing againts fans making one though.
Other than that, I made a new thread here: https://itch.io/t/3449222/questions-gameplay
You can ask pretty much anything gameplay related here and I will try to answer. Other players may answer too.
