LLMs can remember their sources. It's just additional knowledge, there's nothing special about it. When you ask an LLM to tell you the height of Mount Everest,

LLMs can remember their sources. It's just additional knowledge, there's nothing special about it. When you ask an LLM to tell you the height of Mount Everest, it clearly has a map of mountains to heights, in some format. Using exactly the same mapping structure, it can remember a source document for the height.