Wiktionary
no date
n. (context in bibliographies English) (non-gloss definition: indicates that a document has no publication date shown on the document and that none has been inferred from other evidence)
Usage examples of "no date".
I knew that Larry would be there soon, because there could be no date cheaper than to take a woman to a free birthday party, and he said he would be coming with a new Electro-Date.
On March 1, Hitler approved the plan to invade Norway, but set no date for it.