eventually,
One can find out that date through AVM after doing FPs (before any RFE etc.).
For e.g. in my case: I did FPs on 01/04 and AVM says (use to say..) the following...
"On January 17, 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."
That means FBI cleared my FPs on 01/17. Or else once can call IIO to get this info...
- PCee