Probability (The branch of mathematics) has nothing to do with past events. Once an event has happened, the outcome is certain.
Even from a purely semantic standpoint, I think the question is unwittingly changed by knowledge of the past event. For example, if 1000 people enter a raffle, the odds of any randomly selected particular one of them winning (all other things being equal) are 1000 to 1.
However, once the raffle is over and person A has won, some might assert that the 1000 to 1 chance has indeed occurred, at least for person A, but the original question has now subtly been changed..
The original question: “What are the odds of any randomly selected particular person winning” has now morphed into “What are the odds of person A (the actual winner) winning”
The odds of the actual winner winning are, or course, 1. Once an event has happened, the outcome is certain.