I didn't think it was a rule, the person who told me was a 'mother' who spends all her time at BSJA, the daughter is home schooled and does loads of jumping. She will be disappointed then!
It used to be the way...long before British Novice even existed...that you needed to win or be placed to qualify for the second rounds in NC's and Foxhunter. I'm almost 100% certain that it's only 4 DC's that will do it now though