FP expiration - 15 months
Finger Prints do expire within 15 months after the BCIS receives an approved finger-print record from the FBI. Therefore if you have something like, "On June 19, 2002 the results of your fingerprint review for your I485 Application to Register Permanent Residence or to Adjust Status were received, and processing has resumed on your case. We will mail you a notice if further action is needed, or when a decision is made," you can assume safely that yours expires right today! Compare and contrast that the date of reckoning doesn't start with the actual date of finger-print recording, but actual date of receipt of response at BCIS side from the FBI.
I read an explicit article on this regard and that is how I can vouchsafe for my own response. Sorry, unfortunately I do not have that URL to post here.