Any ideas on how you could create a trigger for starting retention when the Event is something like, Period covered by two most recent audits?

We are revising our Records Retention Schedule and one of the classification groups is for auditing by external parties, such as government grants where the government audits our handling of the grant funds.

The classification comments explain that the intent is to keep the two most recent audits on any topic.  

I'm considering removing this Event option from the revision recommendations and just keep these audits for eleven years simply because I cannot figure out how to trigger the retention start date on these odd ball items that could be stored anywhere (in topic folders).  We have too many of these types of audits to have someone just keep an eye out for them!

My retention triggers are mostly set upon documents dropping into folders:  Workflow copies the retention from the folder onto all records dropped into them.

I have triggers for Events on folders for Active/Inactive, where if the project is Active, retention (on the records within) is on hold until the folder field for Active/Inactive is switched to Inactive.

ANY IDEAS?