which represents the mass of the parcels that entered any time prior to \(t\) and will exit at \(t_{ex}\). The \(v_{ex}\left(t,t_{ex}\right)\) is, for any row in the asymptotic She table, the sum over all the columns (all the existing \(t_{in}\le t\)) containing data. They observes also that \(v_{ex}\left(t,t_{ex}\right)\) is essentially unknown at time \(t\) because so are the specifications of the future exit times. Therefore \(v_{ex}\left(t,t_{ex}\right)\) at present \(t\)remains a theoretical construct.
Besides, They suggests to further integrate (3) and (4) to obtain the total mass inside the cv: