Yes, an old HDD can work with a new build if properly configured and updated.
Yes, an old HDD can work with a new build if properly configured and updated.
You were mistaken about that. The system isn't configured for a single machine. I'm confident even Linus mentioned something about this in one of his videos.
I haven't personally used branded Win7 OEMs. What I've read suggests differences between Vista and older versions, and possibly between Win8 and later releases. At least the second point makes sense—avoiding those recovery CDs is smart if you're building a custom desktop.
The BIOS contains the necessary information, and there are many ASUS motherboards available. I don’t really understand how other brands handle this.