The author's formulae leave an interaction out: as the project is delayed, the catch-up costs increase as a consequence. Furthermore, if the delay leads to an u

The author's formulae leave an interaction out: as the project is delayed, the catch-up costs increase as a consequence. Furthermore, if the delay leads to an unanticipated shifting of resources back to the old system to keep it running, that can add to the delay. Catch-up cost has a dependency on undiscovered scope. It is also possible that some of the unknown scope becomes obsolete, but if that is happening, then you are already in a long-drawn-out process.