I don't anyone is really considering this point though- every suggestion, as noble and well intentioned as they are, relies COMPLETELY on people being honest. The "proof in writing" means nothing because it isn't regulated. There are some very well respected reefers (by myself, as well as many others)commenting on this thread. If I get a piece of paper from vendor X stating the coral came from Tyree, what does that mean? What do I/can I do if I doesn't think its correct? Who does anyone believe? Its not as if these "documents" are monitored, validates, or agreed upon by any sanctioning group, so they, in effect, because as valuable only as the paper they are printed on.
I happen to work with captive wildlife quite a bit. In the zoological community, species which are rare, endangered, or limited populations usually have a voluntary managing authority which demonstrates the lineages- exactly as we are discussing here. These SSP (species survival plans), PMP (population management programs), SMP (species management programs), or studbooks keeps detailed and accurate record of the origin of every species within the participating group. For many species (namely SSP), every captive animal in North America, and quite possibly even the civilized world, is noted and "controlled" by this group. This is done for a number of reasons, namely controlling breeding to reduce inbreeding and the subsequent negative effects, but it more or less is exactly what is being mentioned here for corals. However, this system is only as valid and useful as the members which participate in it. Every year, the participating organizations update the inventory, and an assigned voluntary group assesses the population, based on their lineage and history. I am getting a little carried away here, but to make my point, a tremendous deal or organization, cooperation, honesty, and legitimacy, play into this being functional. Trying to do so in a blatantly profit driven system is quite problematic. Heck, look at many of the fashionista clowns that are available today by a very high name captive breeder (I will not name names). These are created by inbreeding selected traits, often of which undesirable, unhealthy, and inviable mutations. But two hunchbacked fish may make a batch that could be should as "quasimoto clowns" for a ridiculous premium. Would people still buy these fish is they knew that it was created with mother breeding son, or sister and brother?
Please understand, I wholeheartedly agree that there should be some registry to regulate the unscrupulous and illegitimate trade which seems to periodically plague this hobby. However, without the coordination and cooperation of everybody in some grand organization, I don't see this as possible. It can, and has been done. Look at MAC certification in collection nowadays,this is exactly the steps towards what we are talking about.