When I was instructing, I had to face examiners for rating renewal and upgrades. There was always a contentious issue that happened to be that particular examiner's pet hobby horse. They would deliberately set that subject for the "long briefing".
When I hit the area of contention and addressed it in my own way, a "full and frank exchange of views" would occur. The fact is that, so long as you can explain - justify - why you've made a certain statement, you won't be failed. Well, not in my experience in Oz, anyway.
So, okay, you've been brought up to believe in four forces. Fine, so was I. I can still argue my case for that now. I can see how someone might want to believe in just three forces and that's also fine by me, so long as they can justify it. I think this is where most examiners are "coming from"... they want to know that you have an understanding of the subject and are not merely doing it parrot fashion.
I think our students have a right to expect that we can explain the particular statement or subject in any of several different ways. I'm not sure that a consideration of three forces makes it any easier for a student to understand because it's still necessary to explain how they are derived. In doing so, one has little choice other than to talk about FOUR forces.
In any event, a verbal P of F exam, which I admittedly hadn't considered in my first post, provides scope to justify your belief, whatever it happens to be.