Luck or something else re bio valve longevity

[Justincwp]

I've been looking for an answer to my valve longevity question and have not came up with any information. Discussions are always about the surgery and recovery but I can't find any information (around the web) as to what factors may or may not influence valve longevity. I have the bio. Maybe there aren't any. Maybe valve longevity is luck. If it is I'll move on and hope for the best. Thanks for any info.
(I can find longevity charts and graphs but never any reasons for failure)