From my understanding of stealth technology (which I must admit is fairly limited), the radar cross-section is merely reduced not eliminated completely. So they

From my understanding of stealth technology (which I must admit is fairly limited), the radar cross-section is merely reduced not eliminated completely. So they could still be detected it was just that the plane might be confused with other common interference. However, I assume in the case of the SR-71, the planes were flying so fast to begin with there was no confusing them for anything, despite of the reduced radar-cross section.