Here is a pretty good explanation of what happens inside a CRT to all of the elements as they age;
http://www.muter.com/English/01BMRRTECH.htm
Rob, I can't remember how manny getters they put in that tube. Perhaps as many as three. I don't have my 15GP22 near the office desk at the moment, so I will check tonight to see how many getters were actually flashed in the neck. I would think they would all degrade at the same rate.
Dave A