The PRD describes the Max Attacks attrtibue of the eidolon like this:
Max. Attacks: This indicates the maximum number of natural attacks that the eidolon is allowed to possess at the given level.
However, a FAQ entry on stacking natural attacks for a synthesist describes it as:
the fused character's natural attacks are still subject to the Maximum Attacks entry in the table for an eidolon of his level. For example, a 1st-level synthesist is limited to 3 natural attacks per round, whether those natural attacks are from the eidolon, the synthesist, or a combination of the two.
So which is it? Is the limit natural attacks made per round or natural attack evolutions taken?
This has a few consequences.
It changes how rake works. The eidolon rake triggers on a grapple check, regardless of whether it starts the turn grappled. If the limit is the number of natural attacks taken, than an eidolon with claws linked to grab can get as many (twice as many technically) rake attacks as it has claws. The more claws it has, the further the number of attacks made can exceed the number of natural attacks taken.
If it's based on the number of attacks made, then it's rules legal to take an evolution that gives two attacks while you posses a number of attacks equal to one below the natural attack limit. The rule is that when you're at max natural attacks you can't take another evolution that grants natural attacks. But if you're one below, and you take two, it doesn't break the limit if you only make your max attacks per round and leave the other one unused. If of course, the limit reflects made rather than taken.
Either way has some odd consequences, but I'm not quite sure which way to come down.
The two statements aren't mutually exclusive.
The number of max attacks an eidolon can have as evolutions is limited to the value from the table.
The faq entry means that a half orc synthestist couldn't stack toothy and the claws from the feat Aspect of the beast (3 attacks) with all of the eidolons natural attacks. (for a total of say six attacks.)
I.e. The combined total number of attacks in a round can't exceed the value from the table even if the synthesist and the eidolon together have more natural attacks.
In your rake example, nothing changes because the total number of natural attacks made in a round can't exceed the table value regardless of where they come from.
The two statements aren't mutually exclusive.
True. One is more restrictive than the other though.
The more I think about it, the more I think it's meant to limit it to attacks per round, but I wish I had more to go on than a sample example in a FAQ addressing a different question.