[AnthonyMouse]

> A critical assumption with large-scale data mining is that past trends continue

Not necessarily. It would be easy to use only recent data and ignore data from decades ago. The prediction accuracy wouldn't go down much as long as there is a large enough sample size in the recent data. It may even go up if the old data really is inapplicable now.

Then if a past trend stops happening, the old data gets purged eventually and only the post-trend data is considered.