For long term stuff, I might add something Arthur C. Clarke said on an episode of the television series, Arthur C. Clarke’s Mysterious World. Though I don’t have the exact quote, it was along the lines of:
Science generally gets to the bottom of things in 50 years &ndash if there’s any bottom of things to get to.
If a claim has persisted for decades without good evidence in its favour, it’s unlikely to ever get good evidence in its favour. Doubtless there are a few counter-examples, but these are rules of thumb, not laws.