Proof is like beauty in that it both must be presented and perceived.
Take that first verse you cited as your proof and let's discuss they ways to view it:
1 Corinthians 6:11
11 And such
were some of you.
But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God.
NKJV
I left it highlighted as you highlighted it.
Do not take offense at my use of the word assume, for we all assume things in our deductions as a means of examining the possibilities.
(1) In your mind you assume that the whole group is faltering in immaturity.
(2) You have therefore assumed then that "were" means the whole group.
(3) And you also then assume that this means they are yet faltering in immaturity and while in that condition are sanctified and justified in Christ.
With all the assuming that is necessary to postulate theories and search for answers we should not be too hard on our self when it turns out we are wrong. Better to be tough on our self about being unwilling to search further, for in many assumptions there is without fail many errors.
1 Corinthians 6:11
11 "And such were
some of you. .........."
[And of that some of you who were but are now not:]
"But
you were washed, but
you were sanctified, but
you were justified in the name of the Lord Jesus and by the Spirit of our God."
That "some of you" completed the three step process of (1) being washed (2) being sanctified (3) being justified.
And therefore they are an example to the remainder who have not yet done so.
You can copy this way of examining your impressions of scriptures if you are willing to struggle a little with trying to see in your mind's eye different ways to look at the verse or verses.
After a while you will have built up a sufficient number of ways to look at each scripture that you will be able to select the undistorted pieces to the puzzle and put the puzzle together yourself.
If I simply tell you, you will hardly believe me because you cannot see it.
Give a man a fish and you feed him for a day.
Teach a man how to fish and you feed him for a lifetime.
There are three directions to look at that verse and I did not elaborate on all of them. For practice try to see it from all of them.
(1) Paul is viewing it as the group yet has many who are yet immature and have not yet completed that three step process. But only "some of you" have.
(2) Paul is saying the whole group is yet immature but have been saved in Christ. (In which case why only "some of you"?)
(3) Paul is saying that the whole group is now mature, washed, sanctified, and justified as the "some of you" that were not, now have become so.
I find (1) to be the undistorted piece of the puzzle.