Synonyms for Dateless (same or very similar meaning)
WordNet sense 1 (having no known beginning and presumably no end):
endless, sempiternal
WordNet sense 2 (having no limits or boundaries in time or space or extent or magnitude):
infinite
WordNet sense 3 (not bearing a date):
undated
WordNet sense 4 (not capable of being given a date):
undatable
WordNet sense 5 (unaffected by time):
timeless
WordNet sense 6 (remaining in an original state):
unaltered, unchanged
From the ODE community, based on WordNet
add/edit