Possible Clues:

• Verifiable thing
• It's undeniable to those characters at the end of 15 across
• It's indisputable
• 'As a matter of ___ . . .'
• Opposite of fiction
• One may be checked on a news show
• Statistic shows calories initially found in lard
• It is so
• Fine deed in truth
• "A dolphin sleeps with one eye open," e.g