Finger print made after 40 does not expire?

A few days ago, my son (14 years old) received his second finger print request (first one was made in May, 2005), but both my wife and I have not received the second request? Does that mean I finger print made after 40 does not expire? or the request letter was lost by the post office? should I call CIS to ask? Does anybody have similar experience?

Thanks! I'm 42 this year, on the first request of finger print, the whole family did together at the same time (May, 2005).