What tamper-evident record means
A tamper-evident record is one built so that changes are easier to detect: originals are kept rather than overwritten, and corrections are dated. The term does not promise a record can never be altered, or that every alteration will show; it means quiet rewriting is harder to hide.
This addresses the credibility question every custody record eventually faces, which is whether it was edited after the fact to fit the story being told. An ordinary notes app can be changed with no trace, so its history is only as trustworthy as the person holding it. A tamper-evident record gives you a way to show how and when it was corrected, which supports your credibility.
Example: if the other side suggests you rewrote your journal to strengthen your case, a tamper-evident record lets you point to its history: when each entry was logged, and which entries were corrected and when.
Whether and how such a record is used in court still depends on your jurisdiction, but a record that shows its corrections openly starts from a stronger position.