Since the announcement in the Thirties (I think) that there was an earthly class, the number of partakers (heavenly class) steadily declined, and they taught that the 144,000 had been all been selected, so there wasn't room for any more. Then the numbers started rising again, and they decided that some who had previously partook, but then left the organization, were not replaced until they died, which explained the rising numbers.
I have been gone a while, so I don't know if the numbers are rising still, or even if they report the numbers now. When I was in, people were skeptical of any new partakers, especially if they were known to have mental health issues, which they often did. My personal feeling is that some people are just prone to altered states of consciousness, and the only way they can make sense of it is to believe they are of the anointed. Of the ones I was well aquainted with, one had anorexia, one was bipolar, one had seizures and one had episodes of fugue states where they acted co mpletely different, childlike and silly, then didn't remember the whole episode later.
They are no longer part of the FDS, they got demoted, now it's just the GB.