Update values from one table to another where key values are not unique I've been trying to figure this out for hours and can't seem to get it. If it can be done, any help would be greatly appreciated! I hope I'm clear with what I'm asking :-)

Consider the following:

Table A consists of lastname (null), firstname(null), merchant, amount, transdate, reference; with only unique field value being reference. The merchant, amounts and transdate can have similar duplicated values. 

example:

Row 1:  {Null},{Null},"BLANK-ROSTER NUM","34.30","2018-01-01","12345" 
Row 2:  {Null},{Null},"BLANK-ROSTER NUM","34.30","2018-01-01","77777" 
Row 3:  {Null},{Null},"BLANK-ROSTER NUM","16.07","2018-12-24","99999" 
Row 4:  {Null},{Null},"BLANK-ROSTER NUM","16.07","2018-12-24","44444" 
Row 5:  {Null},{Null},"BLANK-ROSTER NUM","34.30","2018-01-01","66666" 


The other table has the lastname and firstname values I want to assign to each line, similar merchant,amount and transdate values throughout, but no reference field.

example:

Row 1:  SMITH,JOHN,"BLANK-ROSTER NUM","34.30","2018-01-01"
Row 2:  JONES,JAMES,"BLANK-ROSTER NUM","34.30","2018-01-01"
Row 3:  MILLER,STEVE,"BLANK-ROSTER NUM","16.07","2018-12-24"
Row 4:  WILSON,JACK,"BLANK-ROSTER NUM","34.30","2018-01-01"
Row 5:  DAVIS,BEN,"BLANK-ROSTER NUM","16.07","2018-12-24"


Is there a way to get names updated into the similar rows in TABLE A? It doesn't matter which goes to which so long as one name doesn't populate all similar rows in TABLE A (which is what happens to me). Any row with same merchant, amount, and date can update to any row in Table A that has same merchant, amount, and date. Avoiding the duplication of data is my issue. 

Is it possible to get in TABLE A the names to distinctly assign to a row?

UPDATED TABLE A after assigning names from rows with same merchant, amount, and date distinctly:

Row 1:  "SMITH", "JOHN","BLANK-ROSTER NUM","34.30","2018-01-01","12345" 
Row 2:  "JONES","JAMES","BLANK-ROSTER NUM","34.30","2018-01-01","77777" 
Row 3:  "MILLER","STEVE","BLANK-ROSTER NUM","16.07","2018-12-24","99999" 
Row 4:  "DAVIS","BEN","BLANK-ROSTER NUM","16.07","2018-12-24","44444" 
Row 5:  "WILSON","JACK","BLANK-ROSTER NUM","34.30","2018-01-01","66666" 


//////////Edited to include Table Def using SQL Server 2012

Table A:

 INSERT INTO [Recon2018].[dbo].[RECONReport]
       ([Employee - Last]
       ,[Employee - First]
       ,[MI]
       ,[Posted Amount]
       ,[Merchant]
       ,[Reference]
       ,[transdate])
 VALUES
       (&lt;Employee - Last, nvarchar(50),&gt;
       ,&lt;Employee - First, nvarchar(255),&gt;
       ,&lt;MI, nvarchar(255),&gt;
       ,&lt;Posted Amount, decimal(18,2),&gt;
       ,&lt;Merchant, nvarchar(50),&gt;
       ,&lt;Reference, nvarchar(50),&gt;
       ,&lt;transdate, datetime2(0),&gt;)


TABLE B:

 INSERT INTO [Recon2018].[dbo].[Summary_Final]
       ([Employee Last Name]
       ,[Employee First Name]
       ,[Employee Middle Initial]
       ,[Merchant]
       ,[CLIN Rate (Fee)]
       ,[Fee Transaction Date])
 VALUES
       (&lt;Employee Last Name, nvarchar(max),&gt;
       ,&lt;Employee First Name, nvarchar(max),&gt;
       ,&lt;Employee Middle Initial, nvarchar(255),&gt;
       ,&lt;Merchant, nvarchar(max),&gt;
       ,&lt;CLIN Rate (Fee), float,&gt;
       ,&lt;Fee Transaction Date, datetime2(0),&gt;)
This is impossible. 

+------+------+------------------+-------+------------+-------+
| Null | Null | BLANK-ROSTER NUM | 34.30 | 2018-01-01 | 12345 |
| Null | Null | BLANK-ROSTER NUM | 34.30 | 2018-01-01 | 77777 |
| Null | Null | BLANK-ROSTER NUM | 34.30 | 2018-01-01 | 66666 |
+------+------+------------------+-------+------------+-------+


can't be updated from 

+--------+-------+------------------+-------+------------+
| SMITH  | JOHN  | BLANK-ROSTER NUM | 34.30 | 2018-01-01 |
| JONES  | JAMES | BLANK-ROSTER NUM | 34.30 | 2018-01-01 |
| WILSON | JACK  | BLANK-ROSTER NUM | 34.30 | 2018-01-01 |
+--------+-------+------------------+-------+------------+


There is absolutely no reason to choose Jack Wilson among other persons for the row having 66666 in the last column. Also there is no visible sorting for both tables so we can't use it somehow.