Definitely well known for a long time. I remember seeing an article around 1990 about one of the radar systems that I worked on in the mid-1980s as being able to track the B-2. Both systems were over the horizon radars (very long wave length; antenna arrays stretching for a mile or so). Good tracking accuracy if you looked at it as a percentage of the range but the minimum range was like 400-500 miles (not classified; characteristic of the radar) so even a 1% accuracy means at best a location within 4 or 5 miles. Great for early warning but not useful for targeting. Also, not something that can be made mobile; let alone stuffed into an interceptor.