How long does a cycad leaf live?

I've recently gained interest in growing cycads that are cold-hardy to my area (upstate South Carolina, Zone 7). I'm wondering-- how long do individual cycad leaves live? I have two C. revoluta that have produced new sets of leaves-- one started with five and produced five, the other started with six and produced fourteen. I know that some cycads produce 2-3 "throws" of leaves per year, some 1 or 2, and some maybe produce a new set only every couple of years. And yet I see cycads covered with dozens of leaves. Which seems to imply that individual leaves can live for several years, else how could so many build up when the leaves are produced so slowly?
Can anyone give me an idea of the typical "lifespan" for an individual cycad leaf?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.