Yep your right d6dan and having guided in BC for many goats since 1993 I understand a little how things are set out in BC and as was explained to me lately they also look at the age structure of nannies harvested. Like the link you posted stated, goats start reproduction at 4-5 reaching a peak of maturity around 7.  A 13 year old goat as I shot is on their way out and from what I have read and heard since the harvested my goat more than likely on her last year or two in life(especially with only a few worn teeth left in her) and pretty much 100% a non breeding animal. 
Guess shooting a 3 or 4 year old billy would have been more acceptable to some. I still stand by my decision to harvest an animal that I new was past it prime and leave the younger animals even be it males that are just starting there breeding life. They will be there for possibly the next 6 or so years contributing to the population.
Good to see some are concerned about the populations, and I am also. Leave the breeding animals on the hill and harvest the ones that have done so and are no longer.
SG