In a program, what is the difference between the "Acquisition Date" and the "Member Date"?

I believe acquisition date would be stamped at the time a particular lead is first introduced to your database.  Sort of like 'created date', but specific to a program (as per acquisition program data point).  Whereas member date would just be the date a particular lead was associated with a program, not necessarily acquired by it.

Actually, "created date", "acquisition date", and "member date" all exist in Marketo:

• Created Date is the date the lead first entered Marketo
• Acquisition Date is the date the lead was first attributable to a specific program - not necessarily the created date.  For example, if a lead enters Marketo via a list import and you choose no acquisition program, there will be no acquisition date
• Member Date is the date the lead became a member of a given program.  Leads can be members of many programs.

Thank you!