* The name is misspelled. Perhaps you're thinking of a different author with a similar name.
* The author is not widely published. There might be authors named Seymour Rosen who have published works, but they haven't achieved significant recognition.
* The author works in a specialized field. He might have published works within a specific field, such as academic journals or niche publishing.
To help me find more information, could you please provide me with:
* Any other details you know about the author, such as their approximate age, genre they write in, or any specific titles you remember.
* The context of where you encountered this name. Was it in a book, a website, or somewhere else?
With more information, I can try to help you find the author you're looking for.