Crossword Puzzle Craft whose existence may be denied by government officials, thus proving its existence

Clue: Craft whose existence may be denied by government officials, thus proving its existence

Time of existence (AGE with 3 letters)
Stage of existence (AGE with 3 letters)
"There is no greater ___ than bearing an untold story inside you": Maya Angelou (AGONY with 5 letters)
In existence (e.g. ALIVE with 5 letters)
Have existence (ARE with 3 letters)
Fleece-bearing craft (ARGO with 4 letters)
Golden fleece-bearing craft (ARGO with 4 letters)
Come into existence (e.g. ARISE with 5 letters)
Came into existence (AROSE with 5 letters)
Proving beneficial (AVAILING with 8 letters)