Microsoft Access Not finding correct Linked SqlServer records

Question

Microsoft Access 2010 application is not returning the correct linked records from a SqlServer 2008 database.
For simplicity on the Access side I have a query such as:
column XYZ is defined on the SqlServer as Nvarchar(1);
Select * from LinkedSqlTable where XYZ in ("D","F","X");    
However, it is returning records where XYZ = capital I or capital A only.
If I run a similar query via Management Studio on SqlServer
Select * from LinkedSqlTable where XYZ in ('D','F','X');   
 then the correct D, F or X records are returned.
I have tried using ... Trim(XYZ) in  ("D","F","X");  
                            ...  trim(XYZ) = "D" or trim(XYZ) = "F" or trim(XYZ) = "X";
and in a separate query I have grouped the records to verify the values I am looking for exist and do not have spaces or some special character attached in some way.
I would appreciate any ideas.

Answer 1

 The solution was to setup unique indexes on the SqlServer side, relink the SqlServer table in Access (Link Manager) and the queries seem to be running as needed.   For some reason, copying the linked table to Access, instead of linking, then running
the queries against those "downloaded" table seem to work just fine, even without setting up Primary keys.   As a review, using a Query window via SqlServer Mgt Studio one would set up the indexes as the following (notice a clustered index need all key
fields not to be NULL before a clustered index can be setup.
  Alter Table DatabaseX.dbo.[TableX] Alter Column [Field1]   nvarchar(7) NOT NULL;
  Alter Table DatabaseX.dbo.[TableX] Alter Column [Field2]  nvarchar(2) NOT NULL;
  Alter Table DatabaseX.dbo.[TableX] Alter Column [Field3]  nvarchar(5) NOT NULL;
  Alter Table DatabaseX.dbo.[TableX] Add  CONSTRAINT PK_TableX
        PRIMARY KEY CLUSTERED ([Field1] Asc, [Field2] Asc, [Field3] Asc);
An remember to relink the table on the Access side once this has been accomplished. Thanks for the help.
Bernie OBryan