We typically don't like it when an edit invalidates existing answers. But your question doesn't have any existing answers, so this is pretty straightforward. I would recommend the following:
- Edit the elements of the unknown story out of the question
- Answer the question with the story you know, and accept the answer.
- Post a second story-id question with the elements of the unknown story
To my mind, this arrangement will give you the highest chance of getting a good answer to the question you actually have, while also letting the site at large benefit from the knowledge you've obtained.