Let's take as a given that the Bible is an accurate record of the events 2000 years ago (as your question implies).
Some witnesses of the miracles do not believe in Jesus.
Act 4:16 Saying, What shall we do to these men? for that indeed a notable miracle hath been done by them is manifest to all them that dwell in Jerusalem; and we cannot deny it.
So the Jewish high priest and friends clearly says the miracle was obvious and we cannot deny it, yet their actions clearly show that this did not matter to them, they were not going to follow Jesus or recognize him as the messiah.
This was a miracle of the apostles, but the raising of Lazarus by Jesus has similar elements.
John 11:45-53 Then many of the Jews which came to Mary, and had seen the things which Jesus did, believed on him. But some of them went their ways to the Pharisees, and told them what things Jesus had done. Then gathered the chief priests and the Pharisees a council, and said, What do we? for this man doeth many miracles. If we let him thus alone, all men will believe on him: and the Romans shall come and take away both our place and nation. And one of them, named Caiaphas, being the high priest that same year, said unto them, Ye know nothing at all, Nor consider that it is expedient for us, that one man should die for the people, and that the whole nation perish not. And this spake he not of himself: but being high priest that year, he prophesied that Jesus should die for that nation;
And not for that nation only, but that also he should gather together in one the children of God that were scattered abroad. Then from that day forth they took counsel together for to put him to death.
There was 2 different outcomes to the miracle, some saw and believed in Jesus, others saw, admitted the miracle and set about to kill him.
Perhaps the best evidence of the truthfulness of the miracles is perhaps that the witnesses were willing to die instead of recanting their belief.
No matter what time in history that real miracles are performed, there would be believers and unbelievers in those miracle. Even the Bible itself recognizes this.
John 20:30-31 And many other signs truly did Jesus in the presence of his disciples, which are not written in this book: 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.
Notice the word choice of the translators, that you "might believe".
If you believe in the miracles of Jesus, you are unlikely to believe in those of Mohammad, or Joseph Smith, or those of Zeus, etc. Belief in miracles is a matter of faith -- even when you are an eye-witness.
Thanks to Photoshop and CGI that we see in movies, there is no miracle that could be performed today that could not simply ve dismissed out of hand as computer generated by someone 2000 years from now. Sleight of hand is a further problem. With further technological advances, miracles become even harder to prove -- perhaps expressed in Clarke's Law: Any technology, sufficiently advanced, is indistinguishable from magic.