Cartridge aging and tip wear symtoms?

The 20 year old Fidelity Research Mk1 3f shows no signs of distress when I play track 5,Cartridge tracking tests on the Audio System Test Record(Nat'l Research Council of Canada).
No loss of high end content either.
I think it is wrong to believe that a cartridge will wear out in such a short period of time as 2-4 years.
If handled properly, it should last longer.
You don't suppose the people who sell cartridges might have something to do with this type of audio mind set?
This cartridge I might add has seen service first on a LP12 with a FR12 arm, then an Oracle Delphi with EMT 11 arm,this is a span of 7 yearsof constant use before cd play.
Then it sat in it's box for the next dozen or more years until on a whim I tried it out on a VPI Scout.
I had been into some Grados and forgot why I stopped using the FR.
The best that the cartridge has ever sounded is now on a Rega P9 with the 1000 arm.
Even old scratched lps have less noise than when the cartridge was on the Scout.
I was looking at buying one of the newer mc, but that's not going to happen until this one bites the dust.
So,not all cartridges degenerate over time in my experience.
Maybe the FR's were just well built back in the 70's.
Maybe that's why they went out of business.
I wonder if the Shelter's will hold up like the FR's did.
Same designer.

While I appreciate all the above answers, I am still left confused as to how to recognize the onset of cartridge failure. I agree that if the suspension fails then the results will be probably obvious. However, what are the symtoms of failure of the diamond tip? It seems a little strange to have to remove the cartridge every so often and check the diamond under a microspcope. Assuming that wear is evident under the scope, how long has this been accruing and how much damage has already been done to the record.
If one could recognize diamond wear when it begins and knows the symtoms, it seems to me you could minimize or prohibit record wear.

Diamonds wear very slowly! By the time a diamond would have any significant wear, you would have noticed mistracking *long* before!

Record wear is primarily caused by mistracking- but rarely by a worn stylus! Far more common issues are poor tone arm setup and hardware that is really not up to the task. It is also not a good idea to play an LP more than once in 24 hours, so as to allow for the vinyl to rebound. If you think about it, the amount of pressure that a needle exerts on the LP is prodigious- once you work it out to weight per square inch.

Stylus wear or deterioration of the rubber suspension parts will be most evident from tracking problems. If you hear the music breaking up or sounding sibilant where the sound was clean before, some kind of wear or deterioration may be manifesting itself. A test record with music passages with increasingly higher modulation levels (loudness) are helpful, assuming you can recall how well the cartridge performed on these tests when new. Loud passages, with a lot of high frequency content, particularly toward the inner grooves of the record are the most difficult to track and should show up incipient problems first.

Most microscopic examinations can only detect really gross damage/wear. I've had cartridges examined that were obviously going bad that showed absolutely no wear even when examined under the proper kinds of stereoscopes. The only pictures I've seen that clearly showed subtle wear were those made by scanning electron microscopes and no shop would have access to that kind of gear.

I would go with what I hear to make the call as to when the stylus needs to be replaced.