The scene where Lilith approaches Frasier in the park was actually filmed in Boston Commons, which is across the street from the actual Cheers/Bull and Finch pub.
Frasier comments that Lilith is in her mid 30's. Bebe Neuwirth is one month short of her 34th birthday, at the time of this airing.
Frasier and Lilith married in February, 1988, one month before S6/E21. This episode takes place in November, 1992, three months short of their five-year anniversary. As is common in television series, time is compressed with almost five years becoming seven years. A similar thing was done with the age of Frederick in earlier stories.
This Episode Aired The Week of the 1992 presidential election