Here's an easy answer that'll work some of the time:
If your organization already has in place a job that archives the necessary
things to microfiche or local tape, etc, just modify that job to write the
archive to TSM instead.

I mean, somebody at some point in your organization did some thinking and
said (for example), "At end-of-year, we run mainframe batch job X and save
our accounting reports, etc., and that's enough to meet the legal
requirements."  So just piggyback on that thinking instead of re-analyzing a
complex issue.

If you can.