Frasier states that Woody had been working at Cheers for 15 years. Woody's first appearance on Cheers was in September of 1985. The episode of Frasier aired only about 13.5 years later, in February of 1999.
Daphne starts singing at 15:20, whilst holding a glass of wine. Then we get a shot of Martin looking at her. The moment the shot returns to Daphne, we see her glass being fuller than it was a split second ago, even though a few moments back the bottle was completely emptied into the glass.