DidItShake is a free US earthquake monitor built on official USGS data: a live map of every US earthquake of magnitude 2.5+ from the last 7 days, and a history page for more than 6,000 American places — recent activity, biggest recorded quakes, and long-term statistics in plain language.
Early on, the homepage announced 8 earthquakes in the last 24 hours. The real number was 3. The data was fine; the clock was not. The build had been pinned to a fixed date during development, so every "last 24 hours" count was computed against a frozen moment instead of the real one — and the stale pages looked perfectly plausible.
The fix that actually holds is embarrassingly simple: every generated page now carries its own as-of timestamp, and a pre-deploy check compares that stamp against the real clock. If a page is stale by more than a few hours, the deploy is blocked. One comparison standing guard over every windowed count on the site — because a wrong number that looks right is worse than an obvious error, and on a site people check right after the ground moves, "how fresh is this?" is the whole product.