Undated
/ˌʌnˈdeɪtɪd/
Definition 1 of 1
Pro Tip 1/3Historical Clues
An undated item may be harder to place in historical context, affecting its perceived relevance or authenticity. 
The undated artifact puzzled the archaeologists.
Pro Tip 2/3Interpreting Content
Without a date, infer the timing from the content or source of the information. 
They guessed the undated manuscript was from the early 1900s due to its language.
Pro Tip 3/3Mystery and Ambiguity
Undated works can be intentionally ambiguous, leaving interpretation open to the reader or viewer. 
The artist's undated paintings always sparked intense debate.