Will HBP overly influence the OoP film?

[Catlady (Rita Prince Winston)]

<justcarol67 at ...> wrote in
<http://groups.yahoo.com/group/HPFGU-OTChatter/message/29941>:

<< (I have a little more confidence in Alan Rickman, who refuses to
talk about "Severus," as he calls Snape. I think possibly JKR has
filled him in with regard to Snape's true loyalties. But that won't be
the case with this new writer.) >>

Why so sure that JKR hasn't given this new writer as much information
as she gave Kloves?