Vestal Virgins - What Happens Upon Retirement or Death of an Older Vestal?

Since there's only six vestal virgins at any one time, when do they have to go through drawing these lots or asking for candidates? I assume it's either upon retirement or death of an older vestal virgin. Many people engaged in intrigue to prevent their daughters being included among those in the lottery. Augustus swore that if any of his granddaughters had been of age, he would have put her name forward. So he tries to sort of shame them int putting up some candidates. Everybody's trying to get out of it. This is a bit of an issue that, it seems very particularly the vestals face in this time under augustus.