Then the Sales rep do their usual job of qualifying and converting Leads to Potentials and Contacts. 

I would like to track, still using the CRM API, the evolution of these leads. 

Because the conversion to Potential is done by Sales reps, I don't see how to retrieve a correspondance between Lead and Potential (ids returned by the API are not the same). I could search by name or email address, but these fields can be corrected by the Sales rep, and so, I would loose the correspondance.

I welcome any idea on the issue.

Thanks