You cannot use documents produced on subpoena in one case for any other purpose - such as tendering in a different case. However - once you know they are there you can just issue a subpoena in the new/different case. Look up "Harman undertaking" and you'll find it explained in more detail on the 'net.
It is wonderful to see all of these references to the Trove. The Trove is my favourite aspect of ISX.
RS
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