You are confusing the issue. The dividing line is grey, but most examples fall well too one side or other of the line. If they dont, the business has been poorly advised.
In the vast majority of cases it is clear who will, and will not, succeed.
I dont know the details of this case. However, people go before the General and Special Commissioners for all sorts of reasons. Particularly as concerns the General Commissioners the case often has very little merit.
The Commissioners are often required "simply" to establish the facts. Once the facts are deduced the decision is self evident. On occasions (the more especially before the Specials) the key is a point of law.
Is this case on appeal from the Generals I wonder, or have the parties agreed it may be taken directly to the Specials?
As I said before, unless their is some new pivotal point of law, which I very much doubt, I would be surprised if this case establishes any precedent.