Wikipedia:They can't both be right
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 | This page in a nutshell: Always question changes to values that should be definitive, like dates and numeric values. |
Some types of changes seen while patrolling recent changes are obviously between two mutually exclusive values. When this happens, they can't both be right, and sources should be checked to see if the change introduced factual errors or correct them.
A common type of vandalism is the deliberate introduction of factual errors into articles, and this sort of vandalism is every bit as disruptive as blatant vandalism - perhaps even more so because it can easily go unnoticed for a long period of time if it's not caught when it happens.