Sometimes the following happens: a result is proven, but the author never submits a paper for publication. In some cases, a preprint appears. In some cases, the proof is so short that it can be presented at a conference or lecture series, and the community is convinced. Maybe it later becomes incorporated in the work of others, book or lecture notes expositions appear, other work generalizes or improves upon it etc. The result is widely accepted, and the community gives due credit.
Now assume that some years later, the author decides to submit the paper to a prestigious journal. How should the editor treat it, depending on the circumstances listed above, importance of the result, etc.? The two obvious extreme points of view are "reject, since the result is not new" and "treat the paper as proving a new result with a somewhat delayed submission", but there's a whole spectrum in between, e.g., "what was good for Annals 20 years ago is not anymore, but OK for a lesser journal".
I would be especially interested in precedents that are publicly known or can be shared publicly.