Should a single production run task allow for tracking multiple declarations? How to determine number of rejected pieces by employee?

[Christian Carlow]

Sometimes a work center will receive 16 pieces but split work resulting 
in one employee finishing 12 pieces earlier than the remaining 4 
finished later by another employee. For these cases, shouldn't 
production run tasks support multiple declarations?  How would one track 
which employee is at fault for rejected pieces?