" At any rate, you asked if revelation exists outside of scripture, and John 20 and 21 directly state that yes, there was such revelation given the Apostles."
No, what I said was, "Nowhere does the scripture say that there is a revelation outside of scripture that reveals God's plan of salvation for man or how sinful man can have restored fellowship with Him." There is none. That is what John is saying in John 20:31, "But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name."
There are many things, as John says that are not written, but what is revealed is God's plan of salvation and as Paul states in Gal. 1:6-9, "I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel: Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed."
The point remains that the scripture does not contain a claim of self-sufficiency, but contains indications of other revelations given the apostles. Whether they were necessary or auxiliary for our salvation, we don't know because they were not recorded as gospel. Possibly, they were recorded as non-canonical teaching of the Church fathers.
If the scripture were sufficient for salvation, how did the Christendom survive for decades without the bulk of it, and for centuries thereafter without a definitive canon? What does it do to the Protestants who threw away canonical books because they did not like them?
Yes, there are passages in the scripture that state that the scripture is inspired (all of it, including the parts Luther threw out), necessary for complete clerical education, useful to the point of being the absolute proof for argumentation, and not to be contradicted. This is precisely what the Church teaches about it.