But while it applies to many cells over varied lengths of time (up to many years), it doesn't apply to all cells.
https://www.livescience.com/33179-does-human-body-replace-ce...
https://www.snopes.com/fact-check/does-body-replace-itself-s...
So the idea does apply but not exactly as you claim and it's definitely not absolute, even for atoms, let alone cells.
But while it applies to many cells over varied lengths of time (up to many years), it doesn't apply to all cells.
https://www.livescience.com/33179-does-human-body-replace-ce...
https://www.snopes.com/fact-check/does-body-replace-itself-s...
So the idea does apply but not exactly as you claim and it's definitely not absolute, even for atoms, let alone cells.