Addresses which have been excluded from the duplicate check for certain specific addresses can be included again manually. Addresses are always excluded from the duplicate check in pairs. If you wish to include an address again in the duplicate check, then this address is checked again against all the other addresses which were previously excluded from the check as duplicates of these specific addresses.
You have exluded address A from the duplicate check with addresses B and C. So addresses A and B as well as A and C are not compared with each other. If you now include address A in the duplicate check again, then address A will be compared again with address B and C.
If, for example, you wish to continue excluding address B from the check with address A, then you will have to exclude the addresses from the duplicate check again.
You can include one or more addresses from each list view for addresses or from the Search window in the duplicate check.