Why are there different lists of apostles in different gospels?
The principle reason that there are three different lists of the apostles is that the gospels are independent accounts of the life of Jesus. If they were identical, then why would there be four gospels? If one writer copied from another, then the accounts would not be independent, and would not provide further evidence and witness to the life of Jesus of Nazareth. The fact is that we have four independent or at least nearly independent gospels, which adds greatly to the gospel witness to the ministry of Jesus. The differences in different accounts are generally easily reconciled by common-sense thinking about why one chose to emphasize something different than another. Such applies to the question of the different apostle lists.
So, why are the three lists different? Does that mean that there are errors in the gospels? That seems to be the underlying question. Actually, there are four lists. They are Matthew 10:2-4, Mark 3:13-19, Luke 6:12-16 and Acts 1:13-14. The differences between these lists are small, and are fairly easily explained by the fact that two or three of the apostles were known by more than one name. The apostles who are listed identically in all lists are:
Andrew, Phillip, Bartholemew, Matthew, Thomas, James, Son of Alphaeus and Simon the Zealot.
The differences are as follows, with explanations:
1. Acts does not include Judas Iscariot, because in Acts 1, his replecement by Matthias was described.
2. Peter in Acts is Simon (also called Peter) in Matthew, Mark and Luke
3. James is sometimes called James, son of Zebedee
4. Thaddeus (Matthew and Mark) was also known as Judas, the son of James (Luke and Acts)
5. John was also known as John, the brother of James.
The only identity which is questioned by scholars is Thaddeus being equal to Judas, the Son of James. Being known by two names at that times was not uncommon (as witnessed by Peter/Simon), so this difference is almost certainly not a mistake or inconsistency in the Bible. Given that these gospels were written within thirty years of the life of Jesus, and that many eye-witnesses were still alive at that time, it is very unlikely that mistakes could have entered into the gospel accounts.