Over the course of the series, how long the Loudons had been married kept changing. In an early episode in 1982 they'd been married 16 years; in a 1984 show it was said to be 18 years; when the Loudons are going to renew their vows in 1986 it was said to be 15 years.
The characters "Larry, Darryl, and Darryl," who often waxed philosophical, probably got their names from the main character of the book "The Razor's Edge," by W. Somerset Maugham, Larry Darrell, who traveled the world looking for the meaning of life.
Bob Newhart often made slight references to The Bob Newhart Show (1972) throughout the run of Newhart (1982) Most were veiled, mainly poking fun at the quirks of Dr. Bob Hartley. None of these references ever made any clues to the series finale.
To keep the tabloid press from finding out the real surprise ending, Bob Newhart leaked a "false ending" story for the series, before the final episode was aired. In the "false ending," after being hit on the head by a flying golf ball, Dick Loudon would wake up in Heaven, where he would meet God, to be played by either George Burns or George C. Scott.