There are 2 channels, must count every time either channel passes a slot.
This explains why sometimes the "travel distance" is not even number, but odd.
If it would be always EVEN, than it would be encoder pulses x 2, but for example, this DMC is presenting 633 as travel distance, it will be impossible to be N x 2.
So I would be considering you correct, reading both channels, it is possible to reach an ODD number.