Always tell the truth. That way, you don’t have to remember what you said.

The argument here is practical rather than moral, which is what makes it land. A false account has to be maintained, cross-referenced and kept consistent with everything said since, and the effort continues indefinitely while your memory does not. Honesty is simply cheaper to run. It also means you can stop monitoring who was told what, which is a larger relief than people expect.

If there is a small untruth currently in circulation, correcting it early costs a bad five minutes and ends the maintenance. Later it costs considerably more. The test worth applying is whether you would be comfortable with any two people in your life comparing notes.