Fragnets are only as useful as the discipline behind them.

A few habits separate a fragnet that holds up from one that gets picked apart. Keep them in a separate WBS for project impacts. Reference the source document every time. Use a consistent activity ID structure so anyone can identify the newly added activities and trace the nature of the event. And close the gaps in the timeline instead of leaving room for doubt.

None of this is complicated. It just has to be done every single time.