Somehow I doubt they use any API or API-derived additive schemas. European lubes don't use them either. They've been in business with Lubrizol for so long that I suspect by now Lubrizol maintains and updates a separate repository just for Red Line Oil.
I don't think they do. Yeah, they have a close relationship with Lubrizol. So does Driven, Amsoil, Penngrade, and many others. Lubrizol isn't blending a custom additive package for each of these brands. No additive company does that. They may work together with them on testing different combinations of additives, like Driven and Lubrizol did for nearly 2 years in development of their GP-1 line, but Lubrizol is not blending something custom just for them.
You have basic additive packages that contain your basic AW, FM, EP, and DI additives. They're good for an API approval in that form, or ACEA, or whatever spec the client needs to meet, and they don't have add packs sitting around that don't meet any sort of approval. In the case of Red Line, they get an older (and likely cheaper) API SL add pack to serve as their base. They take polyol ester (most of the reason it's expensive) up to 40% concentration, likely blend in a lot of PAO 4 and PAO 6 to serve as VII and give some cold properties, and blend in whatever else for that particular line/grade. Then they blend in the add pack (API add pack, ACEA add pack, Nigerian Prince Abu-Munjabi Viet-Tokyo Mary Beth Rottenbutt spec add pack, whatever...) and then top treat the additives they want to boost.