Capturing previous info from a field

Here is one way to solve it.    Clients have a problem when ever the sales department changes the Forecast Close date on their Opportunities.   Suddenly $50K disappears from next month and appears a year later.  So the question is what was the last date, who changed it and when?

Not identical to your scenario but pretty close.    Here is the solution:

You make a child table for the info that needs to be reviewed or revisited when it changes.   That way the new info is not really a change, it is actually the last entry.

You make a summary field for the Maximum Record ID of the child table on the parent table.  Then create another relationship back to the Parent using that as the Reference Field.   The current data is then really a look up field coming through that relationship.

You get some interesting conversations when you can point out who made the "change" at 4:22 PM on Tuesday of last week.