What I read is you have FileA and FileB.
You receive a parm with a date and do a DO loop over fileA.
Inside your loop, you process fileB. For every record in fileB, you need to see if a record with that date is in fileA. If so, do not process the record from fileB.
Your concern is that if you use fileA to check for the existence of the record, you will lose your pointer in the initial DO loop.
Is that correct?
If so, all you need to do is to use a different LF over fileA to do the check for record existence. If through both views of fileA will share the same access path, they will have there own pointers in the PAG for you program.