The CP asymmetries necessary for explaining the observed baryon asymmetry of the universe require irreducible complex phases in couplings and imaginary kinematics from loop diagrams. The two conditions still do not guarantee a nonvanishing source term of an asymmetry in the Boltzmann equation, as it may vanish due to the unitarity and CPT symmetry constraints. After a brief introduction to holomorphic cutting rules suitable for tracking these cancellations, we discuss the possibility of generating sufficient asymmetry in the Dirac leptogenesis scenario. The model introduced in arXiv:2404.16934 contains only massless particles and combines the right-handed neutrino freeze-in and the lepton-number asymmetry wash-in. Finally, possible generalization of the CPT and unitarity constraints to thermally corrected asymmetries will be discussed.