Hamster, there seem to be many different views on ISO and JIS interchangeability. I've used both Campa NR and more recent Chorus and Stronglight cranks that have ISO tapered holes with cheap Shimano BB's, and vice-versa, without any issues for many years. Only found out about this in the late 90's because of the articles on Sheldon's site
I've noticed that a lot of people skip the large washer and/or use what ever BB bolt they can find. I'm not saying this explain why you've experienced a lot of failures. But I know this is the reason to many of the failed cranks we saw when I worked in a bike shop.