There are differences in programming between geocoding software. However the actually data used for geocoding by Am Fact Finder, Wiz and FFIEC comes from the same source.
Small differences occur due to one program not being updated exactly as the other. In some cases you may get an exact match on the address, and in others the geocoded is obtained by using the zip+4 code of the same address. This places a location in the center (centroid) of a 7 square block area. So if an address is close to a tract boundary the centroid can be on either side of the street.
As geocoding is not an exact science, as long as you can show you made a determined effort and if your geocode is close to anything the examiners come up with, they will accept it. Neither the the FFIEC or data in Wiz is the absolute gospel of geocoding.
I have been told by legal representatives of FFIEC that their geocoder was never intended to be the end all of geocoding. It was originally provided as an aid to look up more difficult addresses. Banks were supposed to use other geocoding resources (and pay for them) Obviously it hasn't worked out that way.
Compliance Analysis and Research - Software for your CRA/HMDA analysis needs