More specifically, what if an existing constituent donates to a ‘new-to-them’ fund (a fund that already exists in Impact, it’s just that the constituent has not donated to that fund before).  How do those get identified?

A: If a constituent starts donating to an existing fund for the very first time, this would need to be mapped within Impact. You would do so by going to the Fund and search the constituent(s) and then select Add to the Fund.