I use Marketo marketing automation and it syncs leads into CRM automatically (every 5 mins or so).  After a recent webinar, we populated the Most Recent Source Campaign field from Marketo using the relevant campaign GUID from the CRM campaign (and for those where it was their first "touch", we also populate Source Campaign [originating]).  After doing this, only a small subset of leads show in the Campaign > Leads section.  When I look at individual leads, they do have the Most Recent Source Campaign populated, which I assumed would be the tying element to associate them with the Campaign?

Why do only 8 of 99 leads show in the Leads section of the associated campaign?

Another question, once I understand WHAT element places them in this section, I'd like to know if this association is permanent.  I need a way for my sales agents to look historically at a marketing campaign and see the leads and contacts that were part of it (at any point in history).

Thanks in advance!