Kiva was there. He pretty much only appears in the group scenes with a large number of Riders towards the ending though (you can see him among the Riders behind 1 and 2 when their brainwashing is broken), and then gets erased by the Great Leader, never getting any actual camera focus.
Faiz ended with a very open ending, but the implication that Takumi would die soon. Rider 4 basically follows up on the original ending of Faiz, giving it more closure, while also explaining how Takumi could appear in all previous crossovers.
It was technically an alternate timeline even if very close to the main one. Note that Genpachi still was a Shocker monster during Kamen Rider 4.
You know watching a clip of Kamen Rider 3 in the Nininger/Drive crossover credits I saw Kiva in the background so that statement was super redacted after I saw that.
I also still dont understand Faiz at all even after that I suppose I need to put that on the list I need to watch.
All of this alternate timeline stuff when it comes to the movies and such is wild the whole thing with Gou from Nininger/Drive to Kamen Rider 4 is bananas. They can do so much and its low key super canon cause it gets acknowledged in the show at times but it doesn't affect the show BUT ITS SUPER CANON