Cartridge life really only 3 years??

Just to address Sparky's comment directed at me, much of this discussion is an oversimplification. Although suspensions do wear out, stylii do not hit some magic amount of use and become groove gougers. Stylii, as seen under a microscope, wear more like car tires, rounding off the tracking surfaces of the diamond itself. Wear begins on day one and continues until.....the cartridge is taken out of service. So even evaluating stylus wear under a microscope as I have done many times, involves a level of judgement from the person interpreting the visuals except in the case of catastrophic failure where the diamond can actually cleve.

About 8 years ago I called Grado and asked them (maybe it was "He") if I should replace my 25 year old Signature 8, wondering if it had "worn out" or gone flat. The response was no, the coils and magnets do not wear out or go flat. The stylus of course, is another thing. He even offered to check the cartridge out if I mailed it in. I took him up on his offer after which he told me it still sounded beautiful and that I should hold on to it. At some point after that I purchased a Grado Gold reasoning that after 25 years of improvements, a Grado Gold (top of the Prestige series) should sound better than an old Signature. I was wrong. I much preferred the Signature over the Gold. The Signature is still in use today.
That being said, this year I purchased 2 new cartridges, a Grado Reference Sonata1 and a Grado Statement Sonata1 and couldn't believe the refinement I heard compared to the Signature. I guess there's a reason they keep coming out with newer models.
Based on my experience, I don't think cartridges need to be replaced every 3 years because the coils and magnets deteriorate. Stylus use and suspension degradation are another issue entirely.

Counters: yes I have a small manual 'click' (resettable)round metal counter for each TT. Every side, when i use Stylast, I click the counter. Exact, no more guessing. I paid like $5 for each from American Science and Surplus.

It was nice when we had the brick and mortar stores.The best one in my area retired,and didn't do much in home theater. People that didn't even buy anything from him,used to bring their stylus by for him to check it under the scope.He was the last knowledgeable analog dealer in my area.I guess I'm going to need to start keeping track of my play time now too. The big box stores sure don't offer that service,and most likely wouldn't be able to tell the wear on the stylus correctly.