That's assuming there were still stock-parts existing.
I'm not sure how Retro-Bit's uh "factories" or "assembly lines" work, but if they have specific parts used for various controllers, such as "stock parts" for the Sega Saturn Pro Controller, I don't see why they can't use the same stock parts over making brand-new parts they'll need to order en masse for new controllers.
For example, if they made a Dreamcast Pro Controller,
they could make brand-new shoulder buttons exclusively designed for the dreamcast Pro Controller... or, given all the Sega Saturn controllers they make, why not just use shoulder buttons from them?
Granted, I think the shoulder buttons should be marked C and Z instead of L and R but, does it matter?