We know of old supernovae because ancient astronomers catalogued them as new stars (nova means new). Maybe they also managed to find new stars.

The new Vera C. Rubin Observatory should help us with finding new stars and other objects. It will scan the whole southern night sky in three days, marking all changes when it gets to the same patch of sky again.

If sharks have a culture they might have recorded the appearance of Polaris, the north star. Sharks have been longer on earth than Polaris has existed.