Irrelevance of photon events distinguishability in a class of Bell experiments

We show that the possibility of distinguishing between single- and two-phot on detection events, usually not met in the actual experiments, is not a ne cessary requirement for proof that the experiments of Alley and Shih [Phys. Rev. Lett. 61, 2921 (1988)] and Ou and Mandel [Phys. Rev. Lett. 61, 50 (19 88)] are modulo a fair sampling assumption, valid tests of local realism. W e also give the critical parameters for the experiments to be unconditional tests of local realism, and show that some other interesting phenomena (in volving bosonic-type particle indistinguishability) can be observed during such tests. [S1050-2947(99)50709-9].