GM Tube Longevity

I have been testing a new GM tube for the past few days, a Robotron 70 013. Its quite a sensitive tube at around 100 CPM for background count. I got to thinking "would a more sensitive tube last as long as a less sensitive tube" so threw some numbers together to find out. My Initial thought was "if the more sensitive tube clicks more, then surely it wears out faster."

I'm comparing the SBM-20 (~20 CPM background) with the Robotron 70 013 (~100 CPM background)

The SBM-20 has a life of around 20,000,000,000 pulses.
The Robotron has a life of around 60,000,000,000 pulses.

That settles it, right? The Robotron tube has 3 times the life of the SBM-20. Actually, no. When the numbers are crunched it shows a different picture.

First the SBM-20.
20,000,000,000 pulses / 20 (counts per minute for background) = 1,000,000,000 minutes of life
1,000,000,000 minutes / 60 (minutes in an hour) = 16,666,667 hours of life
16,666,667 hours / 24 (hours in the day) = 694,444 days of life
694,444 days / 365 (days in the year) = 1902.5 years of life

Now the Robotron 70 013
60,000,000,000 / 100 = 600,000,000 minutes
600,000,000 / 60 = 10,000,000 hours
10,000,000 / 24 = 416,667 days
416,667 / 365 = 1,141.5 years.

So whilst at first look the Robotron may seem to last longer with it's 60,000,000,000 pulses (3x the amount) compared to the 20,000,000,000 for the SBM-20, the rate at which the Robotron pulses is 5x greater than the SBM-20, thus it will use up all of it's available pulses faster than the SBM-20.

Kinda useless information really, as these tubes will outlast us mere mortals by an order of magnitude, but still a little interesting to know. (at least for me!) I wouldn't ever think a GM tube could last 1000 years running. I would imagine the materials used would start to break down after some time and the gasses would escape much sooner than the maximum pulses have been reached.