To put this event in the data base, D0 had to change its interpretation of one EM cluster from photon to electron, on the basis of muon tagging of the EM cluster. Analysis of events is to some degree a matter of taste. The D0 June 1997 analysis of 6 events, with 3 jets included in 3 jet events, reflects the taste of D0 June 1997 . The fragmentation of a b quark can produce more than one jet because of hard gluon radiation. This corresponds to final state radiation.
Jets can also originate from gluons radiated by partons in the initial state.
We refer to this as initial state radiation. We assign two of them to the b quarks and the third jet either to initial state radiation, in which case we ignore it, or to final state radiation, in which case we add its momentum to that of one of the two b quarks. If there is a jet in the event that is tagged by a soft muon, we only allow permutations that assign this jet to a b quark. There are two ways to pair the momenta of the two charged leptons with the two b quark momenta. Second I do not include all 3 jets in the 3 jet events because I think that Dilepton events should have 2 jets.