
We had this recently with a cruciate ligament injury (we didn't know that's what it was to begin with). The first time we were at the vets about a lameness problem was in February. We didn't make a claim as it was under the excess amount. The symptoms came and went (would disappear for months at a time) over the following months. We mentioned it to the vets on another 2 occassions as a side thing when we were there for other reasons, so again it wasn't claimed for.
It wasn't until December (10 months later) when my dog went in for further investigation and we were referred to a specialist that we then put a claim in. We had noticed a clause about "you must notify us within 180 days of any possible incident which may result in a claim" so phoned (before the xrays etc) to make sure it would be covered as the vets had told us to check when we mentioned the clause to them, as they would have to send the full history. The insurance company said it would be covered as we have a 'life time policy'. I'm not exactly sure what that means though! This is the Kennel Club by the way, and he was insured with them from the breeder and we continued with them so not sure if that is what the 'life time' policy means.
Our vets did say that if the insurance had kicked up a fuss that they would speak to them personally as, like you say, to have to notify them every single time for any treatment would be ridiculous! The problem was never put down as cruciate ligament until last month. Initially it was put as a muscular type injury and then several months later a different vet detected a clunking noise from my dog's right hip so it was put as a potential hip problem (hips turned out to be fine). So, I'm not sure if it might make a difference if it's put down as definitely being a certain condition (rather than a collection of symptoms that could be any number of conditions), that you then don't claim for until beyond the number of days stated in the clause. Hope that makes sense!