COP allowed only 2 combinations this last year in the LP.
There were complaints from the federations, particularly after Plushenko's loss in the Grand Prix final when he threw in a third combination and it diddn't count. Three combinations are supposed to be OK next year.
Under COP, when a skater underrotates a jump, the caller may decide it is an overrotated jump of one revolution less.
So an underrotated 4t may be deemed a 3t by the caller. The same could be true of an underrotated 3t; it could be called a 2t.
The Zayak rule only allows 2 iterations of the same jump, one of which must be in combination.
So the following sort of thing would happen:
Suppose Skater A schedules a 4t by itself, a 3t by itself, and then 4t3t, This is all legal.
However, he underrotates his first 4t, which is called a 3t.
His 3t by itself is now a repeat of a single jump, so it doesn't count under the Zayak rule.
Depending on how the program is written, even if he performs his 4t/3t correctly, it cmight be called a Zayak violation since he already has 2 3t's., because he now has 3 3t's. And he might have no combination either.
There are a lot of screwy possibilities. The ISU is supposed to be fixing this.