Your documentation is incorrect. Unless you book a specific room category, you will never be guaranteed a specific building until you check in, and actually get to your room. For example, if you book Preferred, you will be in buildings 4 or 5 (1960's).
You are correct in assuming buildings 6 and 10 (0) are the 1970's. Make sure to reiterate your requests upon check in.
The reason most folks don't know about building numbers is that it's usually a Cast-only way to refer to the buildings. However, it's really helpful to know, because the first digit of your room number is your building number.