RE: When heaven's door was shut
Joseph Rutherford initially stated that the 144,000 group was complete i.e., sealed back in 1931:
"God having a fixed time for every purpose (Ecclesiastes 3:1), his time to give creatures on earth the opportunity to get in line for a heavenly reward has been from A .D. 29 until, chiefly, 1931, called the "day of salvation". "Let God be True" 1946 ed. p.298
"Although Jehovah had come to his temple in 1918 and had begun judgment of this anointed class, still others must be brought in, because some were found unworthy and they must be replaced. The evidences show that this continued until especially 1931, when there began a work of gathering those recognized as "other sheep" of the Lord Jesus Christ." Jehovah's Witnesses In The Divine Purpose 1959 p.139
Then it was changed with no basis to 1935:
"Hence, especially after 1966 it was believed that the heavenly call ceased in 1935." Watchtower 2007 May 1 p.30
"Their being identified in 1935 as the great crowd of other sheep was an indication that the choosing of the 144,000 was then about complete." Revelation, Its Grand Climax Now at Hand p.125
Then, in 2007 it was changed again,
"As time has gone by, some Christians baptized after 1935 have had witness borne to them that they have the heavenly hope. Thus we cannot set a specific date for when the heavenly hope ends." Watchtower 2007 May 1 p.31″
However, they also cast doubt on anyone who now says they are “anointed”:
"Over the years some, even ones newly baptized, have suddenly begun to partake. In a number of cases, after a while they acknowledged that this was an error. Some have recognized that they partook as an emotional response to perhaps physical or mental strain. But they came to see that they really were not called to heavenly life. They asked for God's merciful understanding." Watchtower 1996 Aug 15 p.31