If I understand correctly you do not want to import the address into RE unless the last gift date from the old DB is after the last gift date currently in RE.
Option 1) Is to set up the profile to import all of the addresses and use the API to check the dates and delete the address information if you do not want to import that one.
Assuming that you have a (simplified) import file with the columns:
Address (would be multiple columns in reality)
olddbLastGiftDate (date of last gift from old DB)
Below I have included some (untested) code to check the last gift date in RE and delete the address lines if the oldDB date is before the current one.
Option 2) Would be to set up the IOM profile to not import any addresses but to output the importID of all of the matched constituents. Then, using the new list of IDs you can use RE query to get their last gift dates and use Excel to match up & compare the dates to make a clean file with only the addresses that you want to import.
**DISCLAIMER** I HAVE NOT TESTED THIS! There are a few areas that will need attention as I have noted in the code.
Public Overrides Sub AfterConstituentOpen(ByVal oRec As Blackbaud.PIA.RE7.BBREAPI.CRecord, ByVal Cancel As ImportOM.API.iCancel)