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Moreover, when the supper is served to individuals, those serving the elements are no less than treating the recipients as if they were in Christ ; though God hasn't given us that information, to again borrow your terminology. My point is that you yourself cannot get around these strictures. We all treat as believers for whom Christ died those who may not be and probably aren't.
Ron,
Our church draws a clear line between believers and unbelievers. The pastor fences the table and unbelievers are warned not to partake of the supper lest they drink and eat condemnation on themselves. They are told they need to repent and believe the gospel. Likewise, our Covenant children who have not yet made a profession of faith are told that they must not partake of the supper .
A good pastor draws clear lines between the saved and unsaved and warns those in danger to repent and be saved. Paul said this to the Corinthians:

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2 Corinthinans 5 Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you? unless indeed you fail to meet the test! 6 I hope you will find out that we have not failed the test.

We all know that there are wheat and tares in the church and it is no charity to give people false assurance of salvation if they are under the wrath of God!

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You must admit that when the pastor addresses the congregation he treats it according to 1 Corinthians 15; in other words he will say to the visible church that Christ died for their sins without knowing for sure.

Faithful pastors will surely make a distinction in application of the text for believers and unbelievers.
Spurgeon would speak to unbelievers at the end of his sermons and tell them the things of comfort and promise do not belong to them if they are outside Christ, and he would warn them that they need to flee to Christ for mercy and for salvation.

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We all treat as believers for whom Christ died those who may not be and probably aren't. Accordingly, you are presuming (again using your terminology not mine) certain people to be converted without knowing for sure because God hasn't given us that information. So, it is not a matter of God imparting to us some special knowledge of who is converted or elect, but a matter of following the biblical paradigm set forth in Scripture. Even Judas, whom Christ knew, was treated by the Lord according to his profession and not possession.

Our church practices discipline to those whose life does not match their profession. Our elders must examine those who want to join the church to discern, as far as they are able, whether their profession of faith is genuine. It would be very irresponsible to do otherwise. Paul expresses his confidence in the validity of the Corinthians' salvation.

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1 Corinthians 1:4 I give thanks to my God always for you because of the grace of God that was given you in Christ Jesus, 5 that in every way you were enriched in him in all speech and all knowledge 6 even as the testimony about Christ was confirmed among you 7 so that you are not lacking in any spiritual gift, as you wait for the revealing of our Lord Jesus Christ, 8 who will sustain you to the end, guiltless in the day of our Lord Jesus Christ. 9 God is faithful, by whom you were called into the fellowship of his Son, Jesus Christ our Lord.