[quote=@Rezod92]
Quick question:

Are Servants allowed to remember the past Grail Wars they've been in? Or, at the very least, feel like they've seen certain Servants way before they were summoned to Fusang?
[/quote]

With the possible exception of Gilgamesh it's less whether or not they are allowed to remember and more whether or not they want to remember something and in how much detail they chose to do so.

Some Servant pick and choose their memories (usually only the things that leave a strong impression) while others simply ignore them all together since they don't feel like they are the same person who potentially might have been summoned a nigh infinite number of times in Grail Wars/etc. throughout all the versions of the Proper Human History.