Write down what the date means
Pair a date with a short description of the event. Keep an anniversary distinct from a related celebration or administrative date. A future reader should be able to understand the entry without guessing why it matters.
Keep uncertainty visible
If you only know a month or year, record that level of precision rather than inventing a day. The calculators require complete dates, so they are not the right way to resolve an uncertain historical date.
Choose a manageable scope
Start with a few meaningful entries and add detail when it is useful. Store private notes somewhere you control. AgeUse can help calculate a span, but it does not keep a timeline or save the dates you enter.