Is the Gospel the same as knowing Jesus' miracles, crucifixion, and resurrection appearances?
No. Knowing Jesus' miracles, the events of His crucifixion, and the resurrection appearances is good but is not the Gospel. The Gospel is the preaching of the cross: while we were yet sinners, Christ died for us and gave Himself for us, as Paul declares.
Les explains that it is good to know all the miracles Christ did among the Jews to prove He was who He said He was, to understand what led to His crucifixion, and to know how they responded to the resurrection in John 20 and 21. But that is not Gospel. The Gospel comes out where Paul comes on the scene, saying Christ commended His love toward us in that while we were yet sinners, Christ died for us, and He gave Himself for us. That is all the man knows—the preaching of the cross. Les notes this is why Paul stresses in verse 16 that though we have known Christ after the flesh, yet now henceforth we know Him no more. He also suggests Paul and Jesus were almost identically the same age, and that Saul of Tarsus heard all about Jesus' miracles and was infuriated, defending his religion and later his apostleship.
Wherefore henceforth know we no man after the flesh: yea, though we have known Christ after the flesh, yet now henceforth know we him no more.
But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.