There's disagreement on them shedding too. Travis Roundy (taxi on the Paunsagaunt) told me that he's picked up velvet sheds from cactus bucks. He also said that his friend, Ryan Hatch (of Muley Crazy) says they never shed. Me personally, I'll never argue with either of them.
I assume in North America a 'cactus' buck is one with damaged testes or a hormonal imbalance?
In Europe they are generally referred to as 'perruque bucks' (wig in french).
My understanding of these(in Roe deer which seem to be 'common' and this is from what ive read and clients Ive guided from Europe) is that some can eventually harden underneath, but generally they will keep growing and eventually die from either fly strike or some form of infection/blood poisoning.
As I understand in some parts of Europe they are highly prized as trophies and has lead to the practice of catching bucks and castrating them.
Never seen one, and they are very rare in Red deer it seems. But from what ive been told from deer farmers is that if you castrate a stag it will stay in the stage its in, ie if you chop him in hard antler he will never shed and re grow, if you do it when hes in velvet he will keep growing and if you do it when hes shed he will never grow anything.
Either way a buck like this one thats been shot is certainly a 'freak' as are most 'world records', but they should be recorded regardless.
Looks to me that some of the points(droppers) are not properly hard yet.
Either way It is what it is, certainly possible Id say for animals to have chromosomal or hormonal disorders that cause extreme growth, happens in people so no reason it cant happen in animals.