Are There Any Good Reference Materials Out There? Help!

I have taken a recent interest in die varieties, and learned a few hard and fast(and expensive) lessons. Many thanks to those of you who have posted helpful answers to some of the dumb questions I've asked. I feel a little more knowledgeable, but still woefully lacking in other areas, the main one being the judgement call..."is it or isn't it"? I bought a Cherrypicker's Guide, and the pictures and descriptions are helpful up to a point, but don't go quite far enough. The main thing I need is a frame of reference. Some overdates are quite obvious and "filled out" with metal. Others seem to be mostly shadows with little sections of metal filling in here and there, but I can't seem to find anything that will tell me "how much meat needs to be on the bone" so to speak, in order for it to be accepted and graded as a true overdate. If this is a chicken and egg question and most of you reading this are cracking up because you've had similar frustrations, that will make me feel a little better, but if any of you can recommend some good reference materials, it would be much appreciated!

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