Here is a great example. There has been a episode of Alaska State Troopers that has been recorded at least 4 times now because there is no guide info...when it was first run it did record as new. But looking at zap2it there is a difference
Previous Episode
Grizzly-pendence Day
S04, E07
The troopers respond to shots fired during a landlord-tenant dispute; a suspect flees on foot into the woods.
Next Episode
Armed & Squatting
S04, E09 (First Aired: December 16, 2012)
Troopers confront a man living illegally on public land; a toddler has disappeared in the woods; a man evades capture in a remote village.
The top one recorded as there is no "first aired" date...the 2nd one which says is on today wont record as its not new