Do you preach the gospel of Luke 9.6
6¶And they departed, and went through the towns, preaching the gospel, and healing every where.?
Yes, sometimes almost the same way they would have and sometimes with more details than they had at the time.
They were preaching from a perspective of the Kingdom that was prophesied in the prophets and they were correct, even though they thought those prophesies were going to be fulfilled in every detail right away. They were still preaching that Jesus had come to heal the sick, cast out demons etc.
I also preach this full Gospel message that the kingdom of God has come nigh unto you and the power of the Holy Ghost is present when I do. People are healed, people are born again, demons are cast out of people and the Kingdom of God is manifest before peoples eyes that the Kingdom Rule of Christ is greater than the kingdom of satan.
People are translated out of the Kingdom of darkness into the kingdom of Jesus Christ as a result of faith when I preach.
So yes I do preach the same Gospel. Jesus Christ and His Kingdom.
I can preach Jesus Christ and His power to set people free from their sins if they repent and believe on Him and people will repent and believe on Jesus and call upon Him and be delivered and saved before they even understand all the details about death burial and resurrection.
Multitudes have been saved by repentance toward God and Faith in Jesus Christ before they understood how the cross figured into God's eternal plan of redemption or why blood had to be shed, or why a resurrection.
If you think people have to have a doctrinal class on the meaning of the cross before they are saved you would be mistaken. Many have been saved by repenting and believing on Jesus and learned about the meaning of the cross afterwards.
You seem to be building your understanding about the Gospel Paul preached, or the Gospel we preach requiring an doctrinal presentation on all the theological points of soteriology and that is why you are thinking that it is a different Gospel because they did not have all those details before the cross. But you don't have to have all those details to preach that Jesus will save his people from their sins do you? You are obsessing over a problem that does not exist except in your own mind. You have created a contradiction when there is none. You have to go back to your original thesis and recognize that Preaching that Jesus will save you from your sins (without explaining how) is in itself the Gospel.