Hi Mel. I think it's a combination of genetics, culture and luck...that you picked a winner!
I know that with each blooming season, you can expect more blooms on the spikes than the years previous. The length of the spikes is another explanation, one I'm not sure of.
I have one doing the same as yours. It's been blooming since February and no signs of slowing down. It's only 3 years old.
ENJOY!
Here's a pic of mine which I just took. (The yellow one cascading down from the top shelf. It's really deep yellow, pic is over-exposed.)