When Sam opens the grate to see where Diane is stuck under the floor, she is seen to be lying from stage right to stage left, perpendicular to the section of the bar where Norm sits. Therefore, when the customer to whom Carla sold a kiss with Diane for $0.50 leans over the grate from stage rear, the camera perspective up from the floor (Diane's perspective) should show him coming from her right. But instead it shows him coming directly at her.
The glove on Sam's left hand is missing in the closeups of Diane in the vent.
The Cheers furnace is out of order and it's supposed to be freezing cold, but the patrons and staff aren't exhaling steam.
When Norm is chasing Cliff, and Carla trips Cliff, her foot does not make contact with Cliff's leg, which would cause him to fall.
Diane's face and clothes are not messed or dirty at all while she's in the vent.