This isn't a case of any sort of metal fatigue, just cold-working (yielding) that produced no crack, so within the rupture limit even as the spoke was severely over-tensioned perhaps 3x or 4x of normal peak cyclical stress. Well-tested in other words, and fully stress-relieved (which the other holes are not). Stress-relieving improves future fatigue resistance, especially in softer metals like this model of rim clearly seems to be made of.
Only if the metal has become significantly thinned would the fatigue issue seem to be a concern, since the cyclic stress level might then be higher.

I can't immediately recall ever seeing a single-walled rim built using washers, but adding one washer or washer stack to optimise the spoke's threading depth makes sense here (though the now-stretched spoke might still need to be shortened and re-threaded if originality is an issue).