Undated (adjective)

1. Not having a date marked on it.
2. Not having a specified or known date.

Origin:

From un- + dated, ultimately from latin dare, "to give".

Examples:

1. The letter was undated, so it was difficult to determine when it was written.
2. The painting was undated, but experts estimated its age.
3. The artifact was undated, but it was believed to be thousands of years old.
4. The manuscript was undated, but it was believed to be from the Middle Ages.
5. The coin was undated, but it was valuable due to its rarity.