The "most ancient copies" were made directly from the original manuscripts and the "most ancient copies" are still in existence. I'm sure you know how the scribes made these copies. So I'm saying nothing was lost of the original manuscripts.
Oh really? How exactly do you know that the oldest copies we have were made from the originals, and not other copies? How do you know nothing was lost, when the originals aren't available to compare with the copies?
That's just plain wrong.
The scripture you quote from Luke is a mistranslation in any case.
The Joseph Smith translation of the scripture reads: "16 And they said unto him, We have the law, and the prophets; but as for this man we will not receive him to be our ruler; for he maketh himself to be a judge over us.
17 Then said Jesus unto them, The law and the prophets testify of me; yea, and all the prophets who have written, even until John, have foretold of these days.
18 Since that time, the kingdom of God is preached, and every man who seeketh truth presseth into it.
19 And it is easier for heaven and earth to pass, than for one tittle of the law to fail.
20 And why teach ye the law, and deny that which is written; and condemn him whom the Father hath sent to fulfil the law, that ye might all be redeemed?
21 O fools! for you have said in your hearts, There is no God. And you pervert the right way; and the kingdom of heaven suffereth violence of you; and you persecute the meek; and in your violence you seek to destroy the kingdom; and ye take the children of the kingdom by force. Woe unto you, ye adulterers!
22 And they reviled him again, being angry for the saying, that they were adulterers."
But even without that knowledge, prophets are spoken of over and over in the New Testament after John the Baptist.
Jesus, for one: Act 3: 22-23 "For Moses truly said unto the fathers, A prophet shall the Lord your God raise up unto you of your brethren, like unto me; him shall ye hear in all things whatsoever he shall say unto you.
23 And it shall come to pass, that every soul, which will not hear that prophet, shall be destroyed from among the people."
And in Luke 7: 16 "And there came a fear on all: and they glorified God, saying, That a great prophet is risen up among us; and, That God hath visited his people."
Matthew 21:11 "And the multitude said, This is Jesus the prophet of Nazareth of Galilee."
He even identified himself as a prophet. Matthew 13:57 "And they were offended in him. But Jesus said unto them, A prophet is not without honour, save in his own country, and in his own house."
Jesus spoke of receiving prophets. Matthew 10:41 "He that receiveth a prophet in the name of a prophet shall receive a prophet’s reward; and he that receiveth a righteous man in the name of a righteous man shall receive a righteous man’s reward."
Paul/Saul is called a prophet: Acts 13: 1-3 "Now there were in the church that was at Antioch certain prophets and teachers; as Barnabas, and Simeon that was called Niger, and Lucius of Cyrene, and Manaen, which had been brought up with Herod the tetrarch, and Saul.
2 As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them.
3 And when they had fasted and prayed, and laid their hands on them, they sent them away."
Judas and Silas were called prophets. Acts 15:32 "And Judas and Silas, being prophets also themselves, exhorted the brethren with many words, and confirmed them."
Those who speak in tongues have prophets to interpret. 1 Cor. 14: 29 "Let the prophets speak two or three, and let the other judge."
Prophets appeared in Antioch and were listened to by the apostles. Acts 11:27-30 "And in these days came prophets from Jerusalem unto Antioch.
28 And there stood up one of them named Agabus, and signified by the Spirit that there should be great dearth throughout all the world: which came to pass in the days of Claudius Caesar.
29 Then the disciples, every man according to his ability, determined to send relief unto the brethren which dwelt in Judaea:
30 Which also they did, and sent it to the aelders by the hands of Barnabas and Saul."
Agabus is again identified as a prophet in Acts 21:10
Being a prophet is a spiritual gift. 1 Cor. 12:28 "And God hath set some in the church, first apostles, secondarily prophets, thirdly teachers, after that miracles, then gifts of healings, helps, governments, diversities of tongues."
Paul seemed to believe there were current prophets when he spoke to the Ephesians.
Eph 3:5 "Which in other ages was not made known unto the sons of men, as it is
now revealed unto his holy apostles and prophets by the Spirit;"
And, in the same epistle: Eph. 4: "10 He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
11 And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers;
12 For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ:
13 Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:"
Are we all in the unity of the faith yet? If not, then there must still be apostles, prophets, evangelists, pastors, and teachers.
James identifies his fellow preachers as prophets. James 5:10 "Take, my brethren, the prophets, who have spoken in the name of the Lord, for an example of suffering affliction, and of patience."
And, of course, two prophets shall appear at the end of the world. Revelations 11:10 "And they that dwell upon the earth shall rejoice over them, and make merry, and shall send gifts one to another; because these two prophets tormented them that dwelt on the earth."
Saying all prophets ended with John the Baptist is simply unsupportable by the New Testament.