And immediately after speaking so to the crowds, he would explain the meaning of his parables to the disciples. Those explanations are also recorded in the gospels.
So let's make sure we make your position clear for the readers at home.
Jesus has His Last Supper with His disciples, during which He establishes the practice of Communion (or the Eucharist, if you prefer). In this, He says "this is my Body, this is my Blood", etc.
RIGHT AFTER the meal and BEFORE leaving the room, Jesus is speaking to His disciples and tells them "I have spoken to you in proverbs..."
And YOUR argument is that Jesus was talking about things He had said to them at other times, but specifically NOT about what He had been telling them just before making that statement, even though a literal interpretation of those statements would have indicated a command from Jesus to violate a Law of God that had been in effect for thousands of years.
Now THAT is a feat of logical gymnastics that would get a 10.0 even from the East German judge!
The immediate context of your quote about proverbs clearly shows the referential context of the proverbs. It is about the returning to the Father, and Messiah's relationship with the Father. Previously there were references to "the door" of the sheep, which he explained. The previous context of this passage, which you partially quoted and then erroneously tried to apply to the Synoptic Gospels, is amidst his sayings about "my Father's house," his unity with the Father, being "the true vine" with the Father as the husbandman. They then became confused when He said He was going away for a little while and they would see Him afterward. He said he would not use the proverb and explain more clearly that He came from the Father, entered the world, would leave the world, and return to the Father. They then agreed He had explained it clearly. 16 A little while, and ye shall not see me: and again, a little while, and ye shall see me, because I go to the Father. 17 Then said some of his disciples among themselves, What is this that he saith unto us, A little while, and ye shall not see me: and again, a little while, and ye shall see me: and, Because I go to the Father? 18 They said therefore, What is this that he saith, A little while? we cannot tell what he saith. 19 Now Jesus knew that they were desirous to ask him, and said unto them, Do ye enquire among yourselves of that I said, A little while, and ye shall not see me: and again, a little while, and ye shall see me? 20 Verily, verily, I say unto you, That ye shall weep and lament, but the world shall rejoice: and ye shall be sorrowful, but your sorrow shall be turned into joy. 21 A woman when she is in travail hath sorrow, because her hour is come: but as soon as she is delivered of the child, she remembereth no more the anguish, for joy that a man is born into the world. 22 And ye now therefore have sorrow: but I will see you again, and your heart shall rejoice, and your joy no man taketh from you. 23 And in that day ye shall ask me nothing. Verily, verily, I say unto you, Whatsoever ye shall ask the Father in my name, he will give it you. 24 Hitherto have ye asked nothing in my name: ask, and ye shall receive, that your joy may be full. 25 These things have I spoken unto you in proverbs: but the time cometh, when I shall no more speak unto you in proverbs, but I shall shew you plainly of the Father. 26 At that day ye shall ask in my name: and I say not unto you, that I will pray the Father for you: 27 For the Father himself loveth you, because ye have loved me, and have believed that I came out from God. 28 I came forth from the Father, and am come into the world: again, I leave the world, and go to the Father. 29 His disciples said unto him, Lo, now speakest thou plainly, and speakest no proverb.
-John, Catholic chapter sixteen, Protestant verses sixteen through twenty nine, as authorized by King James