The Body of Christ isn't some official name. It's a metaphor used by Paul.
Paul also used a building metaphor to describe those in Christ, where Christ Jesus is the Cornerstone, the Apostles and prophets the foundation, and believers as part of the Holy Temple.
Paul also said that HE laid the foundation (which is Christ).
How could PAUL be the ONE that laid the foundation that others were to build upon?
1Cor 3:10 (AKJV/PCE)
(3:10) According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.
Because it was according to the grace of God which was
GIVEN TO HIM.
Paul EXPLICITLY avoided building on those foundations ALREADY laid.
Rom 15:20 (AKJV/PCE)
(15:20) Yea, so have I strived to preach the gospel, not where Christ was named, lest I should build upon another man's foundation:
There are reasons for these statements that you cannot have any chance to understand with your man-made preterist blinders on.