The parameters χ1, 2, which measure nonfactorizable soft gluon contributions to hadronic weak decays of mesons, are updated by extracting them from the data of D, B → PP, VP decays (P: pseudoscalar meson, V: vector meson). It is found that χ2 ranges from − 0.36 to − 0.60 in the decays from D → K̅π to D + → ϕπ+, D → K̅*π, while it is of order 10% with a positive sign in B → ψK, Dπ, D*π, Dρ decays. Therefore, the effective parameter a2 is process dependent in charm decay, whereas it stays fairly stable in B decay. This is in accordance with the picture that nonfactorizable soft gluon effects become stronger when the relative momentum of the decay particles becomes smaller. As for D, B → VV decays, the presence of nonfactorizable terms in general prevents a possible definition of effective a1 and a2. This is reinforced by the observation of a large longitudinal polarization fraction in B → ψK* decay, implying nonfactorizable effects contributing differently to S-, P- and D-wave amplitudes. We found that $A_{1}^{nf}/A_{1}>0>A_{2}^{nf}/A_{2}$, Vnf/V (nf standing for nonfactorization) for B → ψK* decay and $0>A_{1}^{nf}/A_{1}>A_{2}^{nf}/A_{2}$, V nf /V for D → K̅*ρ decay. A measurement of longitudinally and transversely polarized decay rates ΓL and ΓT in colorsuppressed decay modes B̅0 → D*0ρ0, D*0ω and D+ → ϕρ+ is urged.