If he cared wouldn't he of done something that didn't clash with the established cannon?
It's uncanny how much Gentaro resembles me during my school days, everything that happens around him is exactly the same too (and everything that isn't, like monsters attacking and Fourze, is exactly how it would have been).
Renn Kiriyama and Masaki Suda are pretty popular now a days. Not reaching Mizushima or Odagiri status but still appearing in dramas and movies frequently. Still a work of art that they got them to appear in the V-Cinemas.
The first piece of continuity within the Heisei era was the Ore Tanjou movie, the since it was actually part of the series' plot.
After that, it was Climax Deka. Which actually involved two series meeting... But ended up creating a plot-hole on Den-O's side of things (Zeronos using Altair and Vega Form).
Then, the only reason that we now care about continuity is because in Decade it was implied that the original Riders have somehow become aware of, and are in communication with, each other, and the fact that it all ends up with Decade and W teaming up.
Kamen Rider is not based on continuity. Do some of us wish it were? Of course, but not having continuity or screwing with the "canon" concerning to other series it's simply a return to the norm.
(Did not count Ryuki vs. Agito because that was Hyper Battle, and I doubt it was ever meant to be taken into account)