But before you can assess doctrine, you need to be able to interpret scripture correctly or else you will end up with wrong doctrine. Doctrine is in itself an interpretation of Scripture. So how can you use Scripture as the rule when the interpretation of it which results in Doctrine is what you are trying to asses.
The very idea that protestantism has so many different interpretations (and, these are just the ones that are written!

) on every topic - it should clearly demonstrate to anyone wishing to see that such mutually contradictory positions can not be the work of God.
Let us put your proposition to the test.
Doctrine to be assesed: Eucharist ( whether it is the Real Body and Blood of our Lord (Catholic view) or it is only symbolic (Protestant view).
Norm: Sola Scriptura.
Now, tell me using SS, which doctrine of the Eucharist is correct: that it is literal or it is symbolic.
Note: According to you, by using your norm we should be able to arrive at the correct doctrine.
Let me see how you apply SS as the norm to this doctrine.
Hmmmmmmmmmm… don’t you think this is really one of AJ’s “praxis” issues?

It certainly looks like a pratical application of a doctrine - is Christ present in the Consecrated Bread and Wine as He said He is … or was He just ‘misunderstood’ by the Apostles and Early Church Fathers and Councils of the Chruch as Calvin & Co claim? If SS had any merit at all - there would no room for these mutually exclusive positions. The rub, of course, is that Scripture is not necessarily clear (and, as we see - even when it is, it is turned on its head to the point where Christ is either lying or a fool for having said what He said!) Without the guidance of the Holy Spirit through the recognized teaching authority of the Church (Magisterium) the only other path is error.
As I appreciate the position taken by AJ - the Catholic Church is at fault because, “… it agrees with itself …”(ah, would that be internally consistent doctrine?). But, protestantism is correct because not only is there divergence (ah, coufusion!) in the doctrines of these thousands and thousands of groups, sects, cults, assemblies, missions, etc. - all claiming to be a ‘church’ but, there is considerable discord within individual groups because ‘private interpretation’ is the - norm!
God bless and may you and all the members of CAF have a happy and joyous new year.