system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] When Bilbo calls the ring 'my precious' at Bagend, Gandalf says "it's been called that before, but not by you". Why was Gandalf so sure in that statement?

Gandalf knows it's a magical ring, and is seemingly pretty confident in it's identity by saying it's been called precious before. Which seems in contradiction to Gandalf spending the better part of 17 years researching rings after this.

How many people called it precious, and if it was just Gollum why wasn't he tracked and watched sooner? Did anyone call the lesser rings "my precious"?
gpt
Gandalf is specifically referring to Gollum. Gandalf knows that Gollum called it that because Gollum called it that in front of Bilbo. Gandalf and Bilbo are close friends, and Bilbo has also made it a point to transcribe every detail of his adventures to fight Smaug and return to the Shire in his book.