Problem in Dummy field

[#1]

I found a problem ,when i join the 2 table then some of the data being LOST .

But when i used dummy field as shown below then i got the exact figure.

plz help me to understand why the data was lost and HOW is it work(Key1 and Key2)????

LoanInfo:

LOAD AccountID AS AcctNo,

     ApplicationID AS AppRefNo,

     DisbursedOn AS DisbursalDate,

     'LMDummy' AS Key1                                       /* What's the use of this?*/

FROM (qvd);

LEFT JOIN

LOAD Code AS ProductID,

          AppRefNo,

          [New Group] AS Product

FROM

(ooxml, embedded labels, table is Sheet1);

Delinquency:

LOAD (NUM(YEAR(MonthEnd))-1)*12+NUM(MONTH(MonthEnd)) AS MonthEndID,

     DATE(MonthEnd) AS MonthEnd,

     AcctNo,

     POS,

     DPD,

     'Dummy' AS Key2

FROM D:\QV project\table3.qvd(qvd);

JOIN

LOAD AcctNo

RESIDENT LoanInfo; 

/*************************************************************************/

Need your help to understand.....

Thanks & Regards
GC