I'm curious about Geiz 1989 since there was no Rider Series in that year

Huh you're right, I thought it was RX but he's 88

1971 was the Beginning of Kamen Rider
1989 was the End of Kamen Rider Black RX

So series wise it is the beginning and end years. Black RX started in the end of '88 and ended in September of '89

So browsing Wikipedia, noticed the pre-Heisei era being coined as the Ishinomori Era, and you know what? I think we should use it more often when we are referring to riders from Kamen Rider 1 to Kamen Rider J. Cause technically the last Showa rider is RX, which started roughly two and a half months prior to the beginning of the Heisei era, and Shin, ZO, and J were from 92~94, early years of the Heisei era and also the time when Ishinomori was still alive. Just thought I'd share that while it was still fresh in my mind.

You're not wrong. But the term "Showa Rider" has been used for so long and Toei even acknowledged J, ZO and Shin to be "Showa" in Showa vs Heisei, even though it's incorrect historically. So I think we should stick with "Showa Riders"

1989 is the first year of the Heisei era, seeing as Zi-O commemorates its end its significance is pretty obvious.

Yeah, I'm just personally peeved with the idea that Toei bundling the 90s movie riders as Showa when clearly they are not feels like sheer laziness. :lolol
Seriously though Toei should consider regrouping just those three for accuracy sake cause it makes them look ignorant. Call them 90s Trifecta or something. :lolol

More cameos confirmed.

STANDING BY...

https://news.mynavi.jp/article/20180830-686061/

In a post Zi-O world, that adjustment might be a good idea. That's something to save for the overall rider 50th to do though.

There is a rumor (so take with a grain of salt!), that the next series and series after might make cameos in Zi-O.
But the main focus is supposed to be Heisei era only. So don't expect those any time soon, potentially at least not until Zi-O spills over into the next era. Allegedly to tease their future series, or could end up as a write off like Aqua(heh, ride off).

Also a rumor that there may be one more rider revealed for the show later too. But again, nothing solidly proven as yet.

I kinda dig Geiz's outfit, it looks like he raided a Japanese Hot Topic for anything that he thought looked American.