There's a much more ...um... 'credible' way these oddities could exists. They could be the results of controlled and deliberate experimentation.
Let's say that a laboratory is set up to study Aliens. Say, something like the one aboard the Auriga. We know that Aliens take characteristics from their hosts - but hosts can contribute in other ways?
Already in our time can extract DNA from whatever animal we want. Say, a rhino, bull, snake, crab or scorpion... take you pick. Take that DNA sample and inject it directly into the hugger through the egg wall.
We already know that the facehugger specifically fits to a human head so we then allow a human host to be implanted with the hybrid embryo.
The gestation and birthing process may then continue to its completion and the chestburster emerges from the host but instead of growing to become an Alien we have seen in the movies, it adopts the morphology and other characteristics of the DNA that was introduced during the egg stage of its life cycle.
The result being the oddities we see in the form of the Kenner/NECA interpretations.