[isugoo]

My old 08 M3 was a demo. It 2k miles but it ran very well for 4 years of ownership.
I don't know why/how but I've seen total 3 different warranty policy for slightly used but never registered cars from BMW dealership.
You just need to ask them (then your dealer will contact BMW NA to figure it out)

1. Warranty kicked in when they punch it as Demo and no extension for new owner.
2. Warranty kicked in when they punch it as Demo and BMW NA will give you a few months and a few thousand miles as extension.
3. Warranty kicked in when new owner purchased to car. (My M3 had this)

Honestly, I was looking for slightly used 2013 M5s but ended up getting leasing a brand new M5. When I compared 2013 M5 with 9k miles with brand new M5 Competition package (115k sticker), payment was basically the same. And I usually switch cars between 1 - 4 years max. So new worked out better.

Usually brand new they have room to play (for their margin, BMW NA's discount, just to move cars to add sales portfolio, etc.) but I'm not sure they have same room for used or not. BMW NA doesn't care for used sales (unless CPO) so dealership may not play in favor for you. Good luck and keep us updated!