Evidence
Anything used to prove a fact: documents, messages, photos, records or what a witness says.
Definition
Evidence is information presented to a court to establish or disprove a fact in dispute. It includes documents, photographs, digital records, expert opinions, and witness testimony. Courts apply rules about which evidence is admissible and what weight to give it.
In practice
If the period is counted from the day you learned of the problem, write that date down immediately and preserve the original documents.