from Kobashi introduction:

There are three main grades of Ylang Ylang, graded depending on the length of the distillation process. The first is called extra, then three more distillations called grades 1, 2, 3 and complete. Kobashi Ylang Extra is the first part of the distillation. The charged still is run constantly; in the beginning Extra and one are taken, then two and then three. Complete is a mix of the total distillation. Flowers have to be collected every day in the morning some are riper than others.