So, in the Genm special, Gai Amatsu is trying to create a new startup company behind Zaia & Hiden's back when he is infected with the Bugster Virus, which takes the forms of Dan Kuroto & his father, saying that they were summoned & revived by Ark. Nothing really ends up happening, but the Thouser powers turn black (Kuroto says that it's a side effect of Bugster Viral infection) & everyone acts like Ex-Aid & Zero-One take place in the same universe. The issue with this is that, Ex-Aid was only 3 years before Zero-One, but no one in the show seems to know about the Bugster Virus, though the info is readily available to a Humagear. Also, Dan Kuroto doesn't know what a Humagear even is, when we know they were around in this universe at least 10 years before the show, due to Aruto's & Fuwa's flashbacks. So, this would have to mean that Ex-Aid is 40-50 years before Zero-One (Gai is in his 40s), when we know it's not because of the Zi-O crossovers with both.
I would say that this special is entirely irrelevant & pointless, but in the Others: Metsuboujinrai special, the villain takes the form of a black Thouser, then Gai specifically confronts him early on in the movie to ask why the man took his driver. As best as I can guess, this would have to mean that the special is canon. That being said, although the villain in the Others movie has the exact same armor & driver, he uses different Progress Keys to Henshin & calls himself Kamen Rider Zaia, instead of Thouser. I am deeply confused.