Retcons

Throughout the Codename Kids Next Door franchise, various retroactive additions or alterations of the continuity (otherwise known as retcons) have been made. Below are listed some of the retcons made throughout the Classic Continuity, some of which were off-screen information subject to revision.

A retcon doesn't mean that a change is good or bad. A retcon is just new information that imposes a new interpretation of past events. Retcons aren't only limited to the changes that blatantly contradict on-screen information. Things can happen as the result of inconsistencies.

Galactic Kids Next Door

 * As of Operation Interview, it was reveal that there was an entire Kids Next Door branch that exist in Outer Space. It was later change to it being the main branch of the Kids Next Door while the one on earth is a subsection.

Codename Kids Next Door: New Operation

 * According to Operation Archive, the Kids Next Door started when the adults revoked against their child creators. But in the episode, "The First Generation" it was reveal the Kids Next Door was formed sometime after Ben Tennyson discover the Omnitrix and created a negative feedback that was the cause of the creation of the Tennyson's greatest enemy, Vilgax.
 * Characters like Angel and Numbuh 0.3 are now consider alien hybrids when in the original series they were just humans.
 * In Operation Interview, it was stated that Numbuh 1 was the first KND operative from earth that list to be apart of the Galactic Kids Next Door. It was later stated by Spinx, and later Rook, that it was actually Numbuh 362 who they wanted to be in the Galactic Kids Next Door due to her many victory over Vilgax and being on good terms with Azmuth.
 * Grandfather was considered to be the most evil and powerful adult on earth, but it was later reveal to be Ch'rell/Shredder.
 * It could still be possible that Grandfather IS the most powerful and evil person on earth since Ch'rell did not originate from earth, but came to earth sometime during the 18th century.

Pop-Up Retcon

 * Operation Lizzle gave the hint that Lizzle was the first girlfriend he ever had. But it later reveal that Julie was his first crush, but she move away when they were 8.
 * In Nigel 10's universe, Nigel Uno never broke up with Julie as she never moved away thus making it so that Nigel never met Lizzle in school. There's still no reason for how Nigel met his universe's Fanny and Hoagie, but not his universe's Rachel as Nigel in the main timeline met Rachel during their summer vacation which was the same year Nigel met Hoagie and Fanny in Kindergarten.
 * By the time of GKND, the KND haven't met a single alien in real life. However, it was reveal that they knew aliens existed since Rachel turned into those aliens and it was the KND's big secret for several years. They were also there to see Vilgax in person.
 * It was later reveal in, Vilgax Return, that sometime after Rachel took the Omnitrix off, the government mind wipe everybody who knew about Rachel's identity and instead kept it as a government secret. This probably explain why they were so shock to learn that Lizzle was an alien beside the obvious fact that she was consider human for the longest time.