Quick question, the date we're given for the past segments, where abouts in the original series is that?
If you go by airing dates, between episodes 32 and 33. It obviously isn't meant to go there though. Rider 1 and 2 have their final looks, not their initial ones, and there were no Rider scouts by that point.
The movie seems to be meant to take place in the Gel-Shocker period of the series, the last 20 episodes... Well, kind of. General Black is the main enemy and they state that the monsters that appear in the Shocker base have been revived, confirming that the final battles with Ikadevil and Garagaranda had already taken place, and even Ganikomoru, which was the first Gel-Shocker monster defeated by Rider 1. Everything else on the Rider side, like their visual and the scouts, also matches it taking place between one of the last 18 episodes.
The problem is... well, the enemy in the movie was obviously Shocker, not Gel-Shocker - a single look at the grunts shows that. They wanted to stick with Shocker's more recognizable visual elements, like the emblem and the grunts, but wanted to focus on General Black, who hadn't gotten any focus yet in these movies, and so this happened and you have General Black commanding an organization that he actually destroyed in the original series. If they replaced the "Shocker" name and visual elements with "Gel-Shocker" equivalents, the movie would fit in perfectly there.