Correct, as far as we know, because we don't know who the elect are, but God does. From the "Calvinist" pen of the Holy Spirit via Paul concerning this:
Remember Jesus Christ, risen from the dead, the offspring of David, as preached in my gospel, for which I am suffering, bound with chains as a criminal. But the word of God is not bound! Therefore I endure everything for the sake of the elect, that they also may obtain the salvation that is in Christ Jesus with eternal glory. - 2 Timothy 2:8-10
Note, it doesn't say "for the sake of all". So, the "all" of Calvin is qualified, it is speaking of none other than the elect and the preaching is for none other than the elect.