Understanding stored procedure logic

I am not as familiar with PL/SQL as I am with standard SQL and need a little help understanding the below procedure, as I am seeing in the data cases where the data is NOT being updated based on the below, and I'd like to understand why this might be happening.

This procedure package gets called from another program and looks to be updating PARTY_ORIGINAL_SYSTEM_REF and LOCATION_ORIGINAL_SYSTEM_REF per the below, however I have found examples where the data is not updated with the below 'INT018<l_seq_id>' even though it seems it meets the criteria.

My other question is where the object rec_pmt is referring to the same query as the UPDATE statement below it?

PROCEDURE TRANSFORM_PMT_REQ_DATA (p_instance_id  IN  NUMBER, 
                                    p_metadata_id  IN  NUMBER,
									p_sourcefile   IN  VARCHAR2,
                                    p_status      OUT  VARCHAR2,
									p_err_msg     OUT  VARCHAR2
						           )
  AS
    l_seq_id NUMBER;  
	l_intg_code VARCHAR2(240) :='INT018';
	l_counter NUMBER:=0;
  BEGIN
    FOR rec_pmt IN (SELECT DISTINCT PARTY_NAME,ADDRESS_LINE_1,ADDRESS_LINE_2,
	                       CITY,STATE,POSTAL_CODE,POSTAL_PLUS_4_CODE
	                  FROM TGC_INT018_PMT_REQ_FBDI
					 WHERE INSTANCE_ID = p_instance_id
					   AND METADATA_ID = p_metadata_id
					   AND SOURCE_FILE_NAME = p_sourcefile
					   AND INTF_STATUS = 'NEW'
				   ) 
    LOOP
	  SELECT TGC_INT018_PMT_REQ_SEQ.NEXTVAL INTO l_seq_id FROM DUAL;

	  UPDATE TGC_INT018_PMT_REQ_FBDI
	     SET PARTY_ORIGINAL_SYSTEM_REF = l_intg_code||l_seq_id
		    ,LOCATION_ORIGINAL_SYSTEM_REF = l_intg_code||l_seq_id
	   WHERE PARTY_NAME = rec_pmt.PARTY_NAME
	     AND ADDRESS_LINE_1 = rec_pmt.ADDRESS_LINE_1
		 AND NVL(ADDRESS_LINE_2,'1') = NVL(rec_pmt.ADDRESS_LINE_2,'1')
		 AND CITY = rec_pmt.CITY
		 AND STATE = rec_pmt.STATE
		 AND POSTAL_CODE = rec_pmt.POSTAL_CODE
		 AND NVL(POSTAL_PLUS_4_CODE,'1') = NVL(rec_pmt.POSTAL_PLUS_4_CODE,'1')
		 AND INSTANCE_ID = p_instance_id
		 AND METADATA_ID = p_metadata_id
		 AND SOURCE_FILE_NAME = p_sourcefile
		 AND INTF_STATUS = 'NEW' ;
		 COMMIT;
	END LOOP;
END TRANSFORM_PMT_REQ_DATA

There are two possibilities that prevent row(s) to be updated:

1. parameters passed to procedure caused cursor's select statement NOT to return any rows, so update isn't executed at all
2. if cursor returned something, then it is update's where clause that prevented any row(s) to be updated

You said that you

> have found examples where the data is not updated with the below 'INT018<l_seq_id>' even though it seems it meets the criteria

We can't help much as we don't have your table nor data, don't see parameters being passed to the procedure ... nothing. Therefore, you should debug it and make sure that criteria is really met.