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.
Most of the predictions she makes in the books do come true, she’s just clueless about the context of any of it. I suspect dumbledore keeps her around in the castle because she does see from time to time. He’s likely more concerned with keeping others from hearing them than hearing them himself.