Several people have raised or hinted at concerns about 538's presidential odds model, which has Biden favored even though Trump is leading in the polls. For example, https://twitter.com/RiverTamYDN/status/1813906369676001752.

If they just release an update to the model that e.g. changes it, or weakens Biden's chances without admitting anything, this would resolve NO. Looking for e.g. Blog posts or Tweets from 538 or their employees that admit an error.

I will be the judge of what "substantial" means - "we fixed coding errors," change in which polls are included, would all resolve YES. I am not going to bet.