It is well known the "New World Translation" / JW Bible have many serious issues and is corrupted to support JW doctrine. One example is the adding of "other" 5 times in Colossians 1:16-20, so it says, "all other things" instead of "all things" although this is found in no Greek text. This is made to support the JW doctrine that the Father created the Son and then the Son in some way created all other things. This is strongly criticized by many Christians.
The reason I mention this is to point out a great inconsistency. It is true you should not add to the Word, but you should also teach what it says. Christians learn from Colossians 1:16 that the Son is the Creator God. There can be no exception to all things. But what about verse 20? It says it pleased God to reconcile all things whether on earth or in heaven through the Son. Inserting "other" will not make the verse fit ECT (or CI) doctrine any better.
Thanks for asking about Colossians 1:20, which reads:
Col 1:19-20 For God was pleased to have all his fullness dwell in him, and through him to reconcile to himself all things, whether things on earth or things in heaven, by making peace through his blood, shed on the cross.
This verse, taken by itself (not considering the broader context of Colossians and the rest of Scripture) certainly would seem to support universalism. However, there are many other verses which speak of unbelievers perishing (John 3:16), being destroyed in both body and soul (Matthew 10:28), and being burned to ashes (2 Peter 2:6). These passages all certainly seem to teach annihilationism.
As evangelicals, when we see verses which appear to lead to contradictory beliefs, we study and pray and seek God's help to understand how to best harmonize them.
Sometimes we humbly admit that we are not sure what is the very best solution, but we can see possible solutions. I see two possible solutions that harmonize Col 1:20 with what I see as a very clear, strong, consistent, repeated teaching of annihilationism throughout the Bible.
1. The phrase "all things" does not always literally mean "all things" and should be interpreted in each case by the immediate context and the broader teaching of Scripture. For example, Paul writes:
NIV Philippians 3:8 What is more, I consider everything a loss because of the surpassing worth of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them garbage, that I may gain Christ
When Paul says he has lost "all things" (exact same phrase as in Colossians) he does not literally mean everything. Did he lose his ability to speak Hebrew and Greek? Of course, not.
Likewise, we should interpret "all things" in light of the following verses which make it clear that salvation depends on continuing faith in Christ:
Col 1:22 But now he has reconciled you by Christ's physical body through death to present you holy in his sight, without blemish and free from accusation--
23 if you continue in your faith, established and firm, and do not move from the hope held out in the gospel. This is the gospel that you heard and that has been proclaimed to every creature under heaven, and of which I, Paul, have become a servant.
Thus, "all things", when applied to people, means "all people who have faith in Jesus". This is determined by the immediate and broader context.
2. There is another solution which is not contradictory to the one above, but fills it out. This solution fits uniquely well with the belief that the unrighteous really perish, are destroyed, and burned to ashes. This solution says there will come a time when LITERALLY every single thing, including every single human, who exists will be fully and wonderfully reconciled to God. This is because the unrighteous will no longer exist as people able to resist His will, they will have been destroyed and reduced to ashes. All knees will bow to Jesus because the knees of the unrighteous will no longer exist, they will have been burned up into smoke and ashes. This solutions fits all of Scripture as best as I can tell.