This movie and the next take place in an alternate reality ala Star Trek and Star Trek Into Darkness.
- Even though the first three Riders and Shocker are different, the Great Leader has the same voice (Goro Naya) and the Shocker Staff Elderly Gentleman is the same old Dr. Shinigami (thanks to archive footage), so this was clearly once the original Kamen Rider universe before it split off from the one we are familiar with at some point. The original Kamen Rider V3, Shiro Kazami, followed whatever caused the change (like Spock Prime) and took on the name Tobei Tachibana who gives the younger Hongo the Cyclone, explaining why he's portrayed by Hiroshi Miyauchi now.
This alternate reality is an A.R. World called the World of The First.Decade and the Hikari Studio just hasn't found it yet.
- If Hongo's cameo (complete with the same motorcycle) is to be believed, it's the canon world of Kabuto