Hi Klem!
I really worked on my non-dominant hand casting. That and my overhead casting were what I considered to be my biggest "problems." In the end I would say that the loops were pretty close off both shoulders, with the tighter loops going to my dominant hand up. I chose not to reverse cast (off shoulder with dominant hand up--you are allowed to if you wish) except on my overhead cast. My reasoning for this choice was that I have had several students who are lefties and it makes sense to me as an instructor to be able to demonstate and teach with the same hand up that they will use, rather than say"do it like this, only with your left hand up."
I think you should be prepared to cast both reverse and non-dominant. I can do both so I did a few times (for example, doing my dominant hand single spey and then switching to non-dominant, I would reverse snake roll to throw the line upstream so I could demonstrate the left handed cast). If I was an examiner I would ask a candidate to show me both, for the same reason mentioned above.
During my test my examiners (Al Buhr and Denise Maxwell) were very particular about everything I was doing. Early on I made a few good casts but they kept saying "again please." I finally said "ok, but why do you keep wanting me to make two casts when the first one was fine?" To paraphrase the answer, the first one might have been a fluke, so get used to making at least two casts for every task whether or not you nail the first one. The point to my mentioning this is that I really don't think that I would have passed if my non-dominant hand casting was less than very good. You make a few casts off your dominant side and the examiners can see how well you cast, which is a good thing because then you think "ok, they can see that I can handle this stuff" but also a not so good thing if your off-shoulder casting sucks because then they have something to compare. I believe there was a point during my test when they asked me to cast off my dominant shoulder and then do the same cast off my non-dominant side. Fortunately that's how I had prepared so it was "easy" to switch back and forth like that. The difficult thing for me was that I generally cast a very tight loop off my dominant side, so I knew that I would have to get close off my left side in order to make the grade. This is especially problematic with the distance cast because the tendency of course is to use power to compensate for poor technique. Anyways I'm kinda rambling here and doing the stream of consciousnes thing a little but I think that if a candidate casts big rolling loops off their non-dominant side or if they tail off their non-dominant side they probably won't pass.
The interesting thing about non-dominant hand casting is that it really reminds me of how many things I just kinda now do without thinking with my dominant hand up. In a way, it is like learning how to spey cast all over again, and I found it enlightening to teach myself how to cast cleanly with my left hand up. I'd make a cast, then analyse it (loop shape, power, turnover, ease, etc) and then make a few corrections over the next couple of casts, then practice what I'd learned several times to get it started into muscle memory, then make a few notes (sometimes mental, sometimes written) on what I learned so that I could practice it next day.
The "shroud of secrecy"
Interesting observation. I think the oral section certainly has this feel to it, as there are a series of mandatory questions that the examiner must cover and I can understand the concern about revealing them. I won't reveal them, but I personally don't share this concern. As an educator I've found that either a student knows their stuff or they don't, and those who prepare and study will do well whether or not you reveal the questions on the test. In my career in the classroom I've done this many times--given a complete outline of an exam, even the actual questions, and haven't noticed a huge difference in student achievement.
I think a real issue is not the questions themselves, but how well you can answer them, first in a concise fashion and then with additional info if required. Also, your delivery is really important. If you rattle off an answer that sounds like you memorized it from a text book watch out because you can be certain they will ask you for more detail and if you don't have it you're toast.
Anyways, if you think about it the Mandatory Questions should be fairly obvious to anyone who has studied Spey casting in any detail, which is kinda the point of the certification I guess. All of the recommended videos cover these questions one way or the other, and if you think about the questions students are likely to ask or the information you'd want a class to know about Spey casting you'll be well on your way to having the Mandatory Orals. There are also a bunch of optional questions that you could be asked, and I think this is the area where a candidate really needs to understand two-handed casting. Down the raod as more people take the test and the Mandatory Questions get out there I can see the optional questions becoming more like the Mandatory Questions, meaning that if you can't nail the optionals you're dead.
As far as the practical test, as you know it is published on the website so that you can review it. It seems simple to some but it is deceptively so. I know a few very good-to-excellent Spey casters who have not passed, so it is not enough to be a good caster. You need to be well-prepared, and above all clean and consistent. If you cast pointy loops at 80ft you'd better be casting pointy loops at 100ft too. You know that little downwards jump (it's a tail) that happens at the end of a cast? Get rid of it because the examiners are looking for that, which might seem like a little thing and not noticed by most people but the examiners will pick it up. Stuff like that will make all the difference.