I'm pretty sure SOW request is not much different to one or other, if you are able to provide everything at one go, then it goes with that one email. If you happen to have something what need to requested after seeing first, second or third part of docs sent, then just have to keep asking until every piece of information is collected and no open questions left.
For some it's also much more simple than others, if you have everything coming and going to one bank account which you also use for gambling, you get out from there very fast most of the time (of course if you have weird transfers in or out from your account, these will be questioned, whole directive is for AML/CTF where second part is about financing terrorists so some transfers might need explanation if they are from private persons etc...), but many things make it more complicated.
If you have private business (or public, doesn't really matter) there can't any suspicion that you might be using business funds for gambling), especially if you have some business where you use netwallets it's harder to be sure if these are tax declared etc.... some people still don't pay taxes for their income which they take to paypals or skrills. And these netwallets, money is coming to there from somewhere so that statement alone hardly ever is sufficient, your income what you get from your job or business or what ever you do for living is usually information looked for to be sure it covers your gambling.
How ever complicated your SOW can be, you still can manage to send everything at once, spend some time and go through your documents and ask yourself if there are open questions or is everything explained there or need some more supporting documents etc.... It's quite logical process, they want to know where you money is coming and going and it's legit to cover your spending.