18 months, and they can no longer be contacted? Some investment customers don't make purchases for years, can take several years for investments to mature, or need change. SOme business have very long natural lapses between recurring business. And the govt is supposed to decide?
Additionally, the loopholes in this thing were a mile wide! Politicians, pollers, charities, and companies that only called intrastate were exempt. You don't think that the worst of the offenders would have restructured to adapt?
You're not paying attention -- are they active clients or not? If they are active clients, then the 18-month window doesn't apply.
If you aren't contacting your client base at least once per year, if only to confirm that they haven't moved (or died), then I frankly have to question your competence.