but I'm not sure the best way to check that files here have not already been transferred

And by transferred here you mean that file was retrieved to local directory, copied to the third directory, and then removed by some other process, is it? In this case yes, you need to keep log of files which were successfully transferred (or rather just list of files that were copied to the third directory).

In reply to Re^3: Directory comparisons by zwon
in thread Directory comparisons by joeymac

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