Actually the Koni shocks are guaranteed virtually forever-period. IF you happen to not have gotten the C-clips in the grooes correctly or are indeed not properly placing the perch plate or cup over the ring-they can and will eventually pop out.
Koni makes things very easy for their customers-CALL THEM FOR FREE and talk to the experts. If they cannot solve your issue no one will.

I definitely take issue with your position on this excellent brand. WHY-because in over XX years I've NEVER had one fail on either a street car or our race cars. To go even further-I've never sent one in for repairs. They simply are the very best for my money. As I said before-factory support is also excellent.