It seems that are no relation between these fields and the exists-statement - are you sure that the record-count changed. Nevertheless here a very good post about the exists-function: The exists issue.
check for synthetic keys ?
LOAD [@1:3] as Num_Office,
[@5:10] as Num_acct,
//'@1:3'&'@5:10' as [Office-Account],
[@11:160] as Email_Address,
[@161:n] as IDN_UUID,
'Qlikview Export' as Export
(fix, codepage is 1252);
Num_Office&Num_acct as [Office-Account],
IDN_UUID , Export
STORE EDBExport_N INTO EDBExport.qvd(qvd);