Less plausible != impossible.
"Knowing" for me means, that there is no way, that we can be wrong about something. Otherwise it's only "believe", not "knowledge".
It would be good to say the following, instead of "it is so": "So far experiments did never show any sign of identity of photons." (Were there any such experiments?) Oh and what about quantum entanglement of photons? Could that not be interpreted as a sign of identity?