During the OT, it was believed that the dead where in two compartments in the grave ( luke 16 ). Yes, Enoch, Elijah and maybe Moses were taken to heaven, they did not ascend under their own power. When Jesus ascended to heaven after the resurrection, he opened heaven and moved paradise to heaven, Paul in II Cor 12 was caught up to paradise. So, heaven was offically opened up at the ascension after Jesus resurrection, but a few were allowed in before the grand opening. Those referred to as being alive were in the paradise side of the grave.
1 Peter 3:19
By which also he went and preached unto the spirits in prison;
1 Peter 4:6
For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.
Ephesians 4:7-13
7But unto every one of us is given grace according to the measure of the gift of Christ.
8Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men.
9(Now that he ascended, what is it but that he also descended first into the lower parts of the earth?
10He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
11And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers;
12For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ:
13Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ: