This seems to be commonly misunderstood, but Spring Drive and quartz Grand Seiko watches are made by Epson and not Seiko. Many people think that Epson is a subsidiary of Seiko but this is not accurate as Epson has been a publicly traded company that is not managed or owned by Seiko for more than 20 years. There is a lot of (reasonable) confusion around this because the full company name is Seiko Epson Corporation, it was founded with help from the Hattori family, and has a ton of shared history and strong ties between both companies. (See
https://www.plus9time.com/blog/2022/10/22/the-seiko-family-companies-seiko-group-corporation-seiko-epson-corp-how-are-they-related)
It is my understanding that for Spring Drive and 9F Grand Seiko models, Epson manufactures and assembles everything except the bracelet. (I am not 100% sure about the bracelet, but when I visited the factory they were listing off all the components they manufacture and the only thing I noted that they skipped naming were the bracelets.). I am also not sure if they make the hairspring in the 9F movements, or if they are sourced from Seiko as I cannot recall from my trip. (Additionally, hairsprings are a sensitive topic and companies don’t want to divulge too many details on how they are manufactured!)
This also applies to Seiko watches to some degree as well. I suspect, but do not know, that all Spring Drive movements for all brands are manufactured by Epson but I do not know if all quartz movements are also made by them. Notably, the Seiko Astron watches are known to be made by Epson - but I am not sure who manufactures the quartz movements in the other lines of Seiko watches.
Related to this, a few years ago when the Grand Seiko Tentagraph was announced I saw some press comment on how it was strange that Seiko was making a big deal about it being the first-ever mechanical Grand Seiko chronograph when they already had a Spring Drive chronograph model. I suspect that the reason for the marketing around “first-ever” was less that it was a mechanical chronograph but because it was a chronograph made by Seiko themselves.