Once you determined your bearing races were not smooth you should have replaced them. That you had a complete failure after an additional 2-3 thousand miles is no surprise at all. Any time you find damaged balls or races they should be replaced as soon as possible, or, expect the exact result you got. If this happenned to your headset you could have a serious accident when you lost steering. One of the major reasons you do tune-ups/periodic/preventative maintenance is to inspect the bearings and race surfaces. Performance is nice, but safety is nicer.