When Norm is asking Frasier about whether he ever shared anything with Lilith or cried with her, Cliff appears, disappears and then reappears as he shots change.
Even if Frasier had never told Lilith about his past marriage, she still would have had to know, as such information would have been noted on their marriage documents.
After returning to Cheers from the concert, Woody says that Nanny G "kissed some guy in the fourth row," referring to Frasier, who was in the third row.