After reading some more, I might have been wrong about any one particular year. Look over on the m14 forums. Lots of knowledgeable guys over there. Im only 2 years into reloading, so I very well may be mistaken about one year being particularly bad.
BUT, look up case seperation over there and you'll find a fair number of threads on it. Here are some pics from the same batch of twenty I reloaded with 39.5 IMR3031, first reload of this brass. The one is cut in half, you can see the thin spot that I could feel with the paperclip, but it didnt show much in the way of a ring. The bottom one you can clearly see a ring and can feel the dip of the thin spot by dragging the clip from the rim up to the neck. A secong resizing and firing of that shell would have undoubtedly cased a seperation. Three others you could feel dips. Thats 5 out of 20.