Nasuverse Limits on Participants in Grail Wars

[Sect]

Are there any limits on the number or types of participants in the Grail Wars? For example, can there only be seven Servants, with one Servant representing one class?

And this is assuming that the Mages in the War don't cheat.

 

[ttestagr]

Generally there can be only seven, each from a different class . That isn't completely absolute though, as we saw Zouken summon True Assasin. There is also the situation where twin magi summoned two Sabers, I believe in the Third War.

Special circumstances were necessary though.