I now have 13 previous publications under my belt, from short stories to poems, and a novel published online. Yet I still find myself submitting as a 'new' author or 'first-time writer' to most agencies and publishing houses. Even after seeing my credentials I am still considered to be so. At what stage does one cease to be a 'new' author, is there a magical number?
A 'new' writer - in terms of how the publishing industry might define it - is someone without 'credentials'. Credentials can include winning short story competitions and having book reviews published in The Australian (for example) - there are many fledgling novelists who start out publishing journalism in order to build up their credentials. I guess the unspoken rule is that someone else needs to have adjudged your work worthy of publication, which is why publishing online often doesn't count as a credential (if you've published it yourself). And the biggest credential of all is having a book published - so you're technically new until that has happened.
The other aspect of being a 'new' writer is genre: if you're submitting a fantasy manuscript, for example, but the short stories you've had published were all chick lit, you're definitely a new writer in the fantasy genre; your short stories will give you some runs on the board, but not as much as if they were fantasy.