You are wise to select good, reputable suppliers, and stick with them. Keep in mind that there are usually BOTH good and poor parts available from lots of sources. For example, many "New Old Stock" NOS parts you buy today may have been produced only a few weeks/months ago, even though they fit a 40-year old car. AND, the tooling may literally be 40 years old too. Like anything else, tooling wears out. So, you can go to your local GM dealership, and order several parts that may still be available. When you receive them, you may find that some parts may be very good, and others not so good. Want an example? Consider the chrome-plated driver's door outside rear view mirrors on many GM cars of the sixties, including Chevelles. Factory-installed originals for Chevys had a bowtie impression, but GM "NOS" replacements do not today, since only one application now fits Chevys AND other GM cars. That's not always so bad. However, even though it looks very nice, and comes to you in a GM box, you may very well find that the mirror head won't stay in place as adjusted. The slightest vibration from the road will often make them fall out of adjustment. Why? It's because of the worn-out old tooling. So, how is this matter solved today? Fortunately for us, one really good dealer of restoration parts buys up those mirrors in large quantities, tears them apart, "restores" them with some new additional tooling of his own, and then sells them all over the aftermarket to other parts retailers to resell to us, the public. He even mills a bowtie emblem back in for Chevy applications, to make them look correct. BUT, once again, some retailers may prefer to merely buy them direct from GM (at a lower price, you see), and sell them to you as-is. The moral: Find a few good suppliers which you can trust, and stick with them.