A while back you posted material showing that the Catholic translation known as the Rheims version changed the meaning of apostasia in 2 Thess 2:3, to fit their ongoing and growing disputation witht he reformation. The word translated as The Departure through the first several translations suddenly became ‘a revolt’. Then the Protestants, in the rendering of the King James went even further into error translating it as ‘a falling away’ ... I guess trying to ride the fence is not new to human minds.
2 Thessalonians 2:3 Let no one in any way deceive you, for it will not come unless the apostasy comes first, and the man of lawlessness is revealed, the son of destruction,
The word apostasy in Greek is apostasía (from 868 /aphístēmi, "leave, depart," which is derived from 575 /apó, "away from" and 2476 /histémi, "stand") – properly, departure (implying desertion); apostasy – literally, "a leaving, from a previous standing.",[http://biblehub.com/greek/646.htm]
Literally "a leaving from a previous standing." Match that with 1 Thessalonians 4:17.
1 Thessalonians 4:17 Then we who are alive and remain will be caught up together with them in the clouds to meet the Lord in the air, and so we shall always be with the Lord.
And you have Paul talking to the same people about the same issue. The believers "leaving a previous standing" and being "caught up together in the clouds to meet the Lord in the air". As Paul was saying in 2 Thessalonians 2:3 "the day of the Lord" cannot come until the body of Christ is "caught up" and "leaves it's previous standing" on this earth. He was assuring them that that day had not yet arrived.
The term "day of the Lord" always identifies a span of time during which God personally intervenes in history, directly or indirectly, to accomplish some specific aspect of His plan. John found himself in "the day of the Lord" when writing Revelation.