Here is the verse (NKJV)
John 6:39
“This is the will of the Father who sent Me, that of all He has given Me I should lose nothing, but should raise it up at the last day.
1) Does this address those already given, or anyone ever given? Answer - anyone ever given.
2) Does this verse say that anyone has been given (spiritually placed into Christ) at the time Jesus spoke? Nope
What this verse actually says is whenever, past, present or future, God has given an individual to Christ, the Father's will is that Christ will loss none of those given.
Thus John 6:29 does not support election (God giving a person to Christ for salvation) before creation of the entire body of Christ. Calvinism reads that bogus view into the text. Critical reading is a skill apparently in scant supply among the gullible.