In Acts 13.29, Paul affirms that Jesus's dead body was laid in a tomb, and v. 30 says that same body rose out of the tomb, thus leaving it empty. These events took place in AD 48, six to eight years before 1 Corinthians was written. So we know Paul believed in the empty tomb (Jesus's burial in it and resurrection out of it).

Since 1 Cor. 15 is known to be an ancient creed (with a source within 2-5 years of Jesus's resurrection, and since we know the early Christians believed in the empty tomb (Acts 2.29-31).

If we put 2 and 2 together, we get 4. The early Church believed in the empty tomb; Paul preached the empty tomb; therefore we can presume that 1 Cor. 15.3-5 presupposed an empty tomb.

I see this often, but nothing in the verses seems to indicate such a thing. Can someone explain? Why can't the creed presuppose an empty trench grave or mass grave instead?