estimated longevity of various stylus shapes:
- Spherical / Conical - 150hrs
- Elliptical - 250hrs
- Shibata/Line contact - 400hrs
- SAS/MicroRidge - 500hrs
The rest of the story you missed or forgot,
This is not to say that at 500 hrs a SAS stylus is "worn out" - but at that stage the wear has reached the point where distortion at 15kHz surpasses the level specified by Jico for a new stylus. (Which I believe is 3%).
Some manufacturers have traditionally defined a stylus as being "worn out" when it starts to damage the record... in these terms the figures provided by Jico can at least be doubled, and in some cases quadrupled.