Every blog post I’ve read about CIPs boldly claims “beware” of CIP practice as the parent application may be used against the CIP application as prior art.
This is only partly true though. Why? Because, while parent applications can be used against the current CIP application — it only occurs if the CIP has been filed one year after the disclosure. See Santarus v. Par Pharma (Fed. Cir. 2012). For parent applications that have been disclosed by their mere publication, the time to file a CIP is within the first year of publication of the parent application.
Priority claim
It is well know, any claim using the newly disclosed subject matter will be awarded the priority date of the CIP filing. However, the confusion arises when the claim uses subject matter of the parent application but the enablement is disclosed in the CIP. When does this happen? When the parent application did not disclose the enabling features for the claim, but those were subsequently provided in the CIP. In such a case, even if the claimed subject matter belongs to the parent application, the CIP priority date would be awarded.
Is this a problem? Not entirely, but it depends on the situation as to why the CIP was being filed to begin with. As always discuss with your patent attorney whether a CIP filing is best for you.