I have a parent table of events. I have a child table that will have multiple communications about the event. I use a formula field to pull information from the parent to embed into the communication. I want to retain that information - exactly as it was sent. If the parent information changes, it is included in new communications but doesn't change the content of previous communications. For example:
Parent records has "Wedding" for type of event and on 10/16/14 - I sent an email notification stating "Dear John, your Wedding is scheduled for 10/17/14."
On 10/18/2014, I change the type of event to "annulment" and on 10/19/14 - I send an email notification stating "Dear John, your annulment is scheduled for 10/20/14."
What's happening today is that my email notification sent on 10/16/14 changes to "annulment" appearing as if we never informed him of his impending wedding but instead two dates for an annulment.