Is the world getting better at documenting these things, or are they getting more and more common as the world becomes more and more polluted?
How do you mean polluted ? environment ?
I think it's more the % change something goes wrong. There are so many humans being on this planet, it's "normal" that these things start to happen "more" often then when there were less people.
Look at flies (those little pesky ones, we dutchylanders call them fruitflies), there are a lot of those and a lot of "mutants" as well..
It also getting better documented I guess. Many reasons there; law requiring that doctors report this, news sensation selling, cloning still a bit of a hot topic.. (semi related to asian1 post, instead of a donor, grow a clone)