I understand your point that the Thessalonians were troubled because they had received reports that the Day of the Lord had already come. My point is that the nature of the event they believed had occurred is directly relevant to understanding why such reports would be persuasive in the first place.
If Paul taught the Day of the Lord as a universally obvious, world-transforming event, then the claim that it had already happened would be self-refuting. The Thessalonians could simply look around and know it had not occurred. Paul’s response would be, “You can see it hasn’t happened.”
Instead, Paul argues that certain identifiable events must occur first (2 Thess. 2:3-4). That suggests the deception was plausible enough to require theological correction, not merely common-sense observation.
So my reference to a “global catastrophe” is not a non sequitur. It relates directly to the plausibility of the false report. The more publicly obvious the Day of the Lord is assumed to be, the less believable the claim that it had already happened. Conversely, if the Thessalonians could genuinely fear they had missed it, that raises legitimate questions about how they understood the event Paul had previously taught them about.
As I've said, there could have been more falsehood contained in the report than just the lie that the day of the Lord had already come. Why you won't allow for that possibility is beyond me.
But, since you don't accept 2 Peter 3:10-12 as legitimate scripture that can help us understand what will happen on the day of the Lord that will come as a thief in the night, I would assume you accept the book of Luke as being legitimate scripture. Here is what it says in Luke about the day of the Lord, which is the day of the Lord Jesus Christ's second coming when we will be gathered to Him (2 Thessalonians 2:1-2).
Luke 21:25 “And there will be signs in the sun, in the moon, and in the stars;
and on the earth distress of nations, with perplexity, the sea and the waves roaring; 26 men’s hearts failing them from fear and the expectation of those things which are coming on the earth, for the powers of the heavens will be shaken. 27 Then they will see the Son of Man coming in a cloud with power and great glory. 28 Now when these things begin to happen, look up and lift up your heads, because your redemption draws near.”
Like 2 Peter 3:10-12, this describes the coming of Christ as a global event. It talks about "things which are coming on the earth" that cause fear in the hearts of unbelievers. After that passage is when Jesus says what is recorded in Matthew 24:32-34 and Mark 13:28-31 as well.
Luke 21:29 Then He spoke to them a parable: “Look at the fig tree, and all the trees. 30 When they are already budding, you see and know for yourselves that summer is now near. 31 So you also,
when you see these things happening, know that the kingdom of God is near. 32 Assuredly, I say to you, this generation will by no means pass away till all things take place. 33 Heaven and earth will pass away, but My words will by no means pass away.
So, Jesus has established at this point that His coming will affect people all around the earth and that "heaven and earth will pass away" at that time. He was clearly referring to His second coming as being a global event and not a local event like what happened in 70 AD. When you continue reading that is confirmed even further.
Look at what Jesus said immediately after saying that fearful things were going to come on the earth and that heaven and earth would pass away.
Luke 21:34 “But
take heed to yourselves, lest your hearts be weighed down with carousing, drunkenness, and cares of this life, and that Day come on you unexpectedly. 35 For it will come as a snare on all those who dwell on the face of the whole earth. 36 Watch therefore, and pray always that you may be counted worthy to escape all these things that will come to pass, and to stand before the Son of Man.”
See how He is talking about the day coming unexpectedly and how He says to pray to be counted worthy to escape the things that will come to pass on that day? That shows that He was talking about the day of the Lord that will come unexpectedly as a thief in the night, as Paul also wrote about. And He said that "it will come as a snare on all those who dwell on the face of the whole earth.". This shows that Paul was talking about a global event in 1 Thessalonians 4:13-5:3. Using scripture (Luke 21:25-36) to interpret scripture (1 Thessalonians 4:13-5:3), we can conclude that only believers will be counted worthy to escape the unexpected destruction that will come upon "the face of the whole earth" when Jesus comes unexpectedly as a thief in the night while unbelievers "shall not escape" it (1 Thess 5:2-3).
And 2 Peter 3:10-12 confirms that it will be a global event as well. So, with all of this in mind, it has to be the case that the false report not only indicated that the day of the Lord had already come or had already started, but it must have also either misrepresented the scope (global) of the day of the Lord or the suddenness of it.