The relevant part of the NPPG makes it clear that such negative conditions should only be used in exceptional circumstances. They are therefore not going to be a widely used means of avoiding the pooling restrictions.
Whether the rare agreements arising from such negative conditions would or wouldn't count towards the pooling limits is an interesting question. It is arguable that an agreement entered into after a permission has been issued can't be regarded as having been a reason for granting the permission. On the other hand, it is also arguable that the future completion of an agreement, secured by a condition, was a reason for granting the permission.
Ultimately, if put to them, it would be the courts (the new planning court?) that would have to decide the point.
