John Forsythe was never on the set - his voice was recorded, and dubbed in later. He told Aaron Spelling that for him to make an on-screen appearance he would have to be paid a lot of money. Forsythe also never visited the set during the entire run of the show.
Though many believe the detective series Vega$ (1978) is a spin-off of Charlie's Angels (1976), Dan Tanna (played by Robert Urich) was not introduced here, but rather in a Pilot that was aired as ABC TV Movie of the Week on the evening of Tuesday, April 25th 1978. The crossover, (Charlie's Angels: Angels in Vegas (1978)) was simply used to reintroduce the Dan Tanna character and to remind and promote the debut of "Vega$" as an ongoing series, it debuted one week later on Wednesday, September 20th, 1978. The two dates, Tuesday, April 25th, 1978, and Wednesday, September 20th, 1978, differ 148 days equaling 21 weeks & 1 day.
When Farrah Fawcett left the series, her absence was explained by having her character Jill become a professional racing driver on the Grand Prix circuit in Europe. Kate Jackson's absence was explained by having Sabrina getting married and starting a family.
Jill, Kelly and Sabrina were all former members of the Los Angeles Police Department. Kris worked for the San Francisco police and Tiffany was with the Boston police. The only Angel who was never a cop was Julie, who originally was a model.
In the opening sequence of the first season, the city where the Angels attended the police academy was never mentioned. It wasn't until the next season that we found out where the various Angels got their police training.
The original concept of the Angels was to have one brunette, one red-head and one blonde. Kate Jackson was aboard from the beginning of the project and was set to play the lead angel. Farrah Fawcett was the next to join, filling the blonde role, but then the producers dropped the hair color concept and brought in Jaclyn Smith to complete the trio. Ironically, this hair color concept actually came into being when Tanya Roberts (a red-head) joined the show in the fifth season.
When Farrah Fawcett left the series, this began a series of lawsuits in which the producers sued her over breach of contract. However, the suits ended when Fawcett agreed to make a total of six guest appearances the following two seasons, so she would be let go.
Producer Aaron Spelling had also been the producer of the first prime-time TV series with a female private eye in the title role, Honey West (1965) starring Anne Francis. That show may have been ahead of its time, as it only lasted one season. Then in 1976, the public was ready to accept the concept and this series was a runaway hit.
Charlie's Angels was in the top ten for its first two seasons: 1976 - 1977 #5, 1977 - 1978 #4 competing in a three way tie with 60 Minutes (1968) and All in the Family (1971). Midway through Season 3, when Kate Jackson announced her impending departure, the show slipped out of the top ten to #12. When Shelley Hack became Jackson's replacement, the ratings dropped even further to #20. The ratings slide continued and Hack was let go. Tanya Roberts was hired to replace Hack, but the ratings didn't improve; plummeting to an abysmal #59. The show never recovered and was canceled at the end of its fifth season.
John Forsythe was called in at the very last minute to voice Charlie when the original actor who had been cast turned out to have a drinking problem. Aaron Spelling called Forsythe past midnight on a Friday and begged him to come to the studio immediately as the pilot was to be broadcast after the weekend. Forsythe ended up recording his first voice-over in his pajamas.