The IEEE 1584-2018 model range has a minimum bolted fault current (Ibf) threshold (500 A for LV, 200 A for MV).

Let's assume the following calculation methodology was adopted for situations where multiple protection devices were involved in clearing an arcing fault...
Incident energy was calculated after each protection device has operated (i.e. by using the arcing current seen by the device and the corresponding device clearance time), then the total incident energy at the fault location was subsequently determined by summing these calculated incident energy values.

How would you handle the situation where Ibf falls below the 1584-2018 minimum threshold during the above study (e.g. after a protection device has operated and reduced the fault current by disconnecting some generation) and the 1584 equations are no longer applicable?

Would you report the accumulated incident energy up to the point at which Ibf fell below the minimum, or would you adopt an alternative approach?

It sounds like an interesting question but the question could be more clear when referring to the OCPDs as upstream, downstream, or parallels etc. To me, your question begins with them sound like they're in parallel, but your potential solutions sound like maybe they're in series or are series rated.

Following this one.