What tamper-evident record means
A tamper-evident record is one built so that any change leaves a visible trace: originals are preserved rather than overwritten, amendments are timestamped, and deletions are marked instead of erased silently. The term does not promise a record can never be altered; it promises that alteration would show.
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 can demonstrate its own integrity, which is what makes it persuasive when it counts.
Example: if the other side suggests you rewrote your journal to strengthen your case, a tamper-evident record answers with its history: here is when each entry was made, here is every correction and when it happened, and nothing was quietly changed.
Whether and how such a record is used in court still depends on your jurisdiction, but a record that can show it was not manipulated starts from a much stronger position.