This is one of those regularly changing doctrine. Sometimes it is stated that some of the remnant will be on earth when Arm comes, sometimes that they can all have died before it comes.
It was stated back as far as 1878 by Russell that the number was sealed and the rapture was going to occur in that year.
For almost 20 years now the number of partakers at the memorial has been hovering around 8,000.
*** yb97 p. 9 Jehovah’s Witnesses—1997 Yearbook Report ***
As a result, this year there were 12,921,933 present for the Memorial, only 8,757 of whom were partakers.
Obviously this should have rapidly declined as most should now be very old. The Watchtower explains that the number is not declining as being a lot of crazy people partaking that are not really anointed.
*** w91 3/15 p. 21 Who Really Have a Heavenly Calling? ***
Why Wrong Assumptions?
Some may wrongly partake of the Memorial emblems because they really do not acknowledge that anointing "depends, not upon the one wishing nor upon the one running, but upon God." (Romans 9:16) It is not up to the individual to decide that he or she would like to be taken into the new covenant and become a joint heir with Christ in the heavenly Kingdom. Jehovah’s choice is what counts. In ancient Israel, God chose those who would serve as his priests, and he executed Korah for presumptuously seeking the priesthood divinely placed in Aaron’s family....
Therefore, a baptized Christian who in recent years began to think that he received the heavenly calling should give the matter very careful and prayerful thought.
Such a person might also ask himself: ‘Have others influenced me to entertain the idea of heavenly life?’ This would be improper, for God has not assigned anyone to recruit others for such a privilege. A tendency toward fantasy would be no indication of anointing by God, and he does not anoint Kingdom heirs by causing them to hear voices with messages to that effect.
Some might ask themselves: ‘Before becoming a Christian, was I involved in drug abuse? Am I using medications that affect the emotions? Have I received treatment for mental or emotional problems?’ Some have said that they first fought against what they thought was the heavenly hope. Others have said that for a time God took away their earthly hope and finally gave them a heavenly one. But such a procedure is contrary to divine dealings. Moreover, faith is not uncertain; it is sure.—Hebrews 11:6.