See When a Relationship Between Tangible Entities Was Discovered
When you establish a relationship between two tangible entities—for example a person and a location—you can record this in ICM.
When you record the relationship, you can enter the date you discovered the connection.
When you open a case note, you'll see the discovered dates for tangible entity relationships, where these have been specified.
If you export entity relationship data from a case note, you'll see the discovered dates in the exported file.