You said: but a read Matthew indicates otherwise.
Wrong. That is a WAG and not sound biblical scholarship. The verses in Matthew make no statement at all as to whether scripture documents all of Christ’s commands. Nowhere in any part of scripture does it make that claim. The only sense of it is found in John where he indicates that not all that Jesus did is found in scripture. Even if none of the (evidently voluminous) “dids” were commands (which I highly doubt) everything that Jesus did was instructive to His followers and were part of His teaching, were known to His followers and surely handed down to those who followed.
No, it is pure common sense. You are saying that Jesus commanded the disciples to teach more information than could possibly be written down to the ends of the world. It is only feasible if the all these things Jesus instructed the apostles to teach were of small enough quantity to be passed on to other people. Otherwise the apostles would have no idea where to start or what things to mention first. Jesus would have provided a task that would have overwhelmed any human being. I think that is an utterly ridiculous position to have to take.