As always, all of this information comes from the outstanding editors for aio wiki (I'm just transferring their info here).
See also: https://www.aiowiki.com/wiki/Adventures_in_Odyssey#The_.22Split.22_era for more information.
The "Split" era[]
The "Split" era (not to be confused with Split episodes) refers to a time period in AIO history when the producers were searching for a new Whit. In 1994, after Hal Smith died, the character of John Avery Whittaker was sent to the Middle East so the producers could find a new actor to play Whit. To fill the void Whit left, two new characters were introduced. Jason Whittaker, Whit's son who had been introduced in #212: “The Mortal Coil, Part 2”, portrayed the adventurous side of Whit. He also possessed Whit's inventing skills. Whit's wisdom and faith were found in the other new character, Jack Allen. Jack and Whit were lifelong friends, and Jack took over Whit's "grandfatherly" attributes, aiding the kids in moral dilemmas and being the spiritual leader of the gang at Whit's End. The attributes of Whit were split between Jason and Jack and the show continued on.
Departure of Will Ryan[]
Between 2000 and 2005 Eugene Meltsner was almost nowhere to be found. While he was involved in the Novacom saga, he never actually spoke during these shows. Only things about him were mentioned, like the fact that his apartment had been ransacked (#484: “Plan B, Part 1: Missing in Action”). This absence of Eugene was due to the absence of Will Ryan, the actor who played Eugene. While it is not known (to the public) why Will Ryan went on this hiatus, one can guess it may have dealt with contractual issues or family problems. Eugene and Will Ryan returned in 2005 in #564: “A Most Intriguing Question”. The absence of Eugene was explained by saying that he and Katrina had toured the world. Eugene has been on the show steadily since that date.
Novacom and new directions[]
The Novacom saga was a major series in AIO. The saga lasted between 2000 and 2002. It dealt with the evil doings of a broadcasting company named Novacom, Andromeda (the parent company), and all of their minions such as Bennett Charles. They planned on using mind control to rule the world (clearly showing the view of the AIO writers and producers). During this saga, Whit opened a new Whit's End in Connellsville. Many new characters were introduced then cut after the series ended in the spring of 2002. During this series, Robert Mitchell (Mitch), who was allegedly murdered, but later found to be alive, was introduced and he and Connie became a couple. Cal Jordan ([|Alex Jefferson]]'s cousin) was also introduced. Jason became a more prominent character, but after the end of the Novacom series, he returned to his minor role that he had before the series began. Cal and Mitch exited soon after the end of the Novacom series as well. Aubrey Shepard and her family was also largely cut after this Novacom saga. Another major outcome from the saga was the tone of the show. The Novacom series was very mature for the usually young audience (8-12 yrs. old), with most episodes posting the usual warning to that effect. While the Novacom saga is a favorite of many Odyssey fans young and old, AIO has been quite different ever since. In general the tone has been much lighter hearted with little of the intrigue found in during the Novacom days.
Album 51[]
Album 51: Take it From the Top was a new beginning for Odyssey fans. Paul McCusker described it as "a fresh beginning so that the older fans could continue listening to the same old characters, and for the new fans, a way to introduce Odyssey to them without having to go back to the first album."
The Green Ring Conspiracy[]
The Green Ring Conspiracy, a saga similar to Novacom, introduced a few new characters to Odyssey, including Penny Wise and Buck Oliver. The saga centered on a counterfeiting ring in the town. Penny and Buck went on to become regular (even major) characters on the show, with Penny as Wooton Bassett's love interest and later his wife, and with Buck as Eugene and Katrina's foster son.
Jason's Departure[]
Jason Whittaker was still living in Odyssey at the end of Album 50, and still had a "nemesis" out looking for him. In #634 – #635: “Accidental Dilemma”, Jason is confronted by this nemesis ("The Whisperer") and the episode ends with the Whisperer arrested, Jason safely in hiding, and the rest of Odyssey believing him to be dead. Jason's character did not appear in Album 51 or Album 52, but he returned, undercover, in #686: “The Green Ring Conspiracy, Part 8” (Album 53). He played a major role throughout the rest of the album, and did not appear again until #703 – #705: “The Labyrinth” in Album 55. Jason still did not assume a normal role in Odyssey until Album 56 (fall 2012), where he took ownership of the J & J Antique Gallery from Jack and Joanne Allen. This proved to be providential, as the actors for Jack and Joanne (Alan Young and Janet Waldo, respectively) passed away in 2016.