In Fate/Zero it seems to be implied that all the Masters, from the moment they started working with them, knew the identity of their Servants.
i known however that
- in Fate/Stay Night
- Shirou didn't learn Saber's identity until much later because it was feared that if he was captured he wouldn't be able to defend against mind reading magic
- Rin didn't learn Archer's at first because the summoning went wrong and messed up his memories however he continued to withhold it when he did remember who he was
- in Fate/Extra
- Hakuno didn't know the identity of his/her Saber, Archer or Caster until the final couple of weeks but i am not sure how many of the Masters they faced off knew their Servant's Identities at the start (though i get the feeling Rin, Leo and Rani knew)
so in all the Grail Wars (Fuyuki (Fate/Stay Night), Snowfield (Fate/Strange Fake), Moon Cell (Fate/Extra), Trifas (Fate/Apocrypha), Tokyo (Fate/Prototype), Caubac Alcatraz's Labyrinth (Fate/Labyrinth) etc.) where there any other Master who didn't know their Servant's identity at the beginning? if not at all?