The secret science of pub months

I am curious as to which months Australian publishers prefer to publish fiction in, especially debut fiction, and which months they like to avoid. From what I've found, Australian publishers tend to avoid December. Why is that? And October appears to be the most popular, for reasons unknown to me. Are there months that are a "no go", months that are considered "average" and months that are considered "popular" for debut fiction, established fiction and so on? This is a "publishing mystery" to me and any light shed on this would be ... well, enlightening.

When an author receives an offer for their first book I usually spend some time explaining why the book is not going to be published in certain months of the year, and why that means their novel is being published, say, 18 months hence. It can sound all very confusing, but the science of publication schedules is not that difficult to explicate.

The cardinal rules are:

Christmas books come out in October and November - no earlier, no later;
Mothers' Day books come out in April, and May at a push;
Fathers' Day books come out in August, and September at a push.

These are the big book retail selling periods.

My question back to you is: why would anyone publish anything in December? What do you think is happening in December? People are rushing around getting ready for Christmas. Are they going to stop and buy a first novel? No. They want to buy the sport and cooking books, the Bryce Courtenay, Di Morrissey and Matthew Reilly novels, that have been appearing in stacks since October. They may well have spent October and November doing their gift research and now they're purchasing. What they're not doing is buying a novel from someone who is not Bryce, Di or Matt. And if you're a novelist, why would you want to compete with that troika? You'll get obliterated. And you certainly won't get any publicity, because the pre-Christmas book publicity is taken up by the 'gift books'. Ergo, December is a bad idea. So are October and November, unless you are an already established author. I don't know of many publishers who would publish debut fiction in those months, unless it's written by Adam Gilchrist.

Debut fiction usually comes out in January, February or March, and occasionally September. Obviously there are exceptions according to the author's public profile - if you already have a profile then the novel could come out in May (for Sydney Writers Festival) or August (for Melbourne WF). June and July used to be a possibility but there are so many writers festival now that the middle of the year is crowded, publicity wise. Debut fiction is incredibly hard to publicise, even if the author has a great personal story, so publishers will choose months that are otherwise quiet. The beginning of the year is good because it's summer holidays and they can sometimes score interviews for their new novelists, plus there's less competition for review space.

So it's not that mysterious, really. And perhaps some of it is just habit, but those sales cycles are well established and everything revolves around them.