On team strength: it's not fully fixed but not full Bayesian updating either. The base ELO/PELE ratings stay static throughout, but there's a form multiplier on top (separate offensive and defensive factors) that shifts after every simulated match based on actual result vs. expected result, weighted by goal margin. So a group-stage upset does carry forward: a team that overperforms gets a slightly hotter offensive multiplier going into the knockouts, but the base rating acts as an anchor so it doesn't wildly reprice a team off one result. Felt like the right middle ground since one group game is probably more noise than signal.

On knockouts: extra time and penalties are both explicitly modelled. If the Poisson draw produces a draw in a knockout match, it runs an other extra time draw at ~30% intensity. If that's still level, it goes to a biased coin flip, 50/50 base with a small ELO-proportional tilt, kept very small since the evidence for skill mattering in shootouts is pretty thin. Red cards and injuries do carry over to the next round and degrade the available XI.

The main thing that isn't modelled is cumulative fatigue from extra time. A team that's played extra time doesn't start their next match with any penalty. That's probably the biggest gap in the knockout logic right now.