... the pool of people potentially to offend (ie people and companies taking submissions, especially in Australia) is so small and so apparently interconnected, the possibility of getting it wrong seems like a big risk to take -- is it unreasonable to fear that a mistake will affect all your future submissions as well as the current one? It seems hard to condemn someone for overthinking it, the way it is in the publishing industry at the moment.
And the answer is: yes, it's unreasonable. The reason I say that is that the publishing industry - as monolithic and impenetrable as it seems - is not a collective of vindictive individuals, let alone individuals who have enough time and brain space to remember the name of each author who sends in a submission, the better to be able to give them a black mark for a future submission. Nor do we discuss submissions with each other. So while, yes, the industry is interconnected - as many are - we don't tend to conspire.
So for those of you who are submitting now or in the future, or who have submitted in the past and not been successful, please bear this in mind: in almost 100% of cases rejection isn't personal to you, the author. It is about your work. If the rejection is personal, then it means you have already had some kind of interaction with an agent or publisher and it's not working out for whatever reason, and thus the relationship is severed, regardless of what the work's like. But usually it's the work.
Accordingly, when you're planning to submit, ensure that your work is the best it can be. Then do your best with the query/submission letter and the synopsis if these things are requested. All you can do is your best. Everyone in the publishing industry understands this. And we won't know if you're not doing your best, of course, because we don't know you; so we presume that you do your best and make a decision accordingly.
If you have not done your best, do not be surprised if you're rejected - you haven't given yourself much of a chance, so why should an agent or publisher give you a chance? This reaction, by the way, is not evidence of malice on their part.
Finally, before submitting, work out what sort of person you are: the sort who believes that things happen to them because everything is against them and they can't control what happens - the 'why me?' or 'God hates me' type - or the sort who believes they have some kind of agency in their own fate. Because this, more than anything, will determine how you handle the submission process and the inevitable rejections - which the vast majority of published authors have received, by the way, at some stage of their career.
You can make your work the best it can be but still be a 'why me?' type who is going to fall at the first hurdle; you can submit work that is not your best but also be a person who believes that they can have control over their own life. The ideal combination is to be a writer who makes their work the best it can be and also be a person who believes that things that happen to them are not the result of a malevolent force that's out to get them. Both of these things are within your control. Both of them affect your ability to succeed at what you want to do. Being a successful writer - however you define that - takes talent and application. Mostly application. And application is also within your control.