I would actually suggest otherwise, that either Decade or Zi-O was subsumed into the other’s tag and Kiva remains separate. Even Wataru’s presence in Decade is (officially, but it’s stupid so I ignore it) considered to be yet another AR (alternate Rider) counterpart. The strongest ties are undeniably between Zi-O and Decade, and Tsukasa even temporarily serves as both a tertiary Rider and villain general in Zi-O. Kiva was the last standalone season until… Zero-One, 11 years later. Or else all three could be merged into KR Heisei Era