Correct, it was. According to Rev 1:18, Christ "holds the key to Death and Hades." Therefore only Christ can free those in "Death and Hades." He freed the believers in the first century and they preceded those believers who were alive and remaining at the time. We agree on this, I think?
So, what about the unbelievers? Are they still in Death and Hades? According to Dan 12:2, "Some (rise) to everlasting life, Some to shame and everlasting contempt." This happened in very close proximity to the "time of trouble" AKA, the "great tribulation" of first century Israel. Michael stood up and protected the believing Jews, the "sons of (Daniel's) people." So what about the dead?
According to John 5:29, there is a "resurrection of life" and a "resurrection of condemnation", echoing the lesson in Daniel 12. Acts 24:15 teaches the same thing, "there will be a resurrection of the dead, both of the just and the unjust." Thus we have three witness passages teaching the same thing, that those dead, both good and bad will rise again AT THE SAME TIME. The John 5 passage is very clear about this and as to the timing:
"...for the hour is coming in which all who are in the graves will hear His voice 29 and come forth—those who have done good, to the resurrection of life, and those who have done evil, to the resurrection of condemnation."
Thus both resurrections occurred at the same time, around 70 AD, during the "parousia of Christ" (which many of our uninformed brothers and sisters view as the future second coming). Now the Daniel 12 passages says "many of those who sleep in the dust of the earth shall awake." He doesn't say "all" will awake. Isn't that interesting?
The only passage I am aware of that might be suggesting something different is in Rev 20:5. Who are the "rest of the dead (that) did not live again until the thousand years were finished?" I have some theories. Dying to hear your thoughts on this.