A notable aspect of Sybill Trelawney’s character is that she has no recollection of the prophecies she has made. Is it possible that she has made other prophecies which no one happened to be around to record? She seems to spend most of her time alone in her tower.
Yes, why not? Outside of what’s written in the books, as long as the author doesn’t write something that contradicts it, you can speculate and imagine as much as you want. Only the author can give you a definitive answer.