How to Find Where/How a Microsoft Custom Field Is Used

[megweber221]

My team recently discovered a Microsoft Custom Field in our Marketo instance called "Marketo Inactivity", but we don't know how users have been marked with this field as "True". We want to know what parameters were used (batch campaign, trigger campaign, etc.) to mark users as such.

When we run the smart list "Marketo Inactivity = True", we see that 34,000 people are on the list, so they had to have been marked with this field somehow. But when we search the field in Field Management in Admin settings, it says it's only being used by the smart list mentioned above, no batch campaigns or trigger campaigns. 

Is there another way to figure out how users have been marked with this Marketo Inactivity field as "True"? Do we need look in Dynamics or is there another place to look in Marketo?

[SanfordWhiteman]

If the changes were made in the past 90 days, then a Smart List on Data Value Changed will tell you the source.

After 90 days, you don’t have a reference point.