Excel formulas showing wrong old numbers — silent broken link
A formula linked to another workbook is showing a number that hasn't matched reality in a while, with no error at all. Excel is quietly displaying the last value it cached from that external file. Here's why, and how to check
Why there's no error even though the link is broken
Excel doesn't re-fetch external references every time a workbook opens by default — it caches whatever value it last successfully pulled from the source, and displays that cached number until it's told to update the link again. A missing or moved source file breaks the ability to refresh that value, but it doesn't erase the cache, so the formula keeps confidently showing the last good number rather than switching to an error state.
How to check if this is happening near you
Open Data > Edit Links (called External References in some versions) to see every external reference in the workbook, along with its source path and status — a status of Unknown or an unreachable path is a strong sign that any formula pulling from it is showing stale, cached data rather than a live value. It's also worth checking whether "Don't display the alert and don't update automatic links" is turned on for the workbook, since that setting is exactly what suppresses the prompt that would otherwise warn you a source can't be reached.
Fixing it: reconnect or convert to a static value
If the source file still exists somewhere, use Edit Links > Change Source to point the reference at its new location and force a fresh update, which pulls the current value in place of the cached one. If the source is gone for good, use Edit Links > Break Link to convert every formula that referenced it into a plain static value — just be aware that this locks in whatever the last cached number happened to be, so confirm that number is actually correct before you break the connection permanently.