The Patent Cooperation Treaty (PCT) system provides several routes through which an applicant may seek to correct or amend aspects of an already filed PCT application.
Rule 91−Rectification of Obvious Mistakes in the International Application and Other Documents
When it is necessary to correct an obvious mistake within the description, claims or drawings, an applicant may refer to Rule 91. Under this rule, within 26 months from the priority date an applicant may submit a request wherein they specify the mistake to be rectified and the proposed rectification. The applicant may, also, provide a brief explanation of the mistake to be rectified and the proposed rectification.
When taking advantage of Rule 91 it is important to remember that what constitutes an obvious mistake subject to rectification is very narrowly defined to a mistake “obvious to the competent authority [where] something else was intended than what appears in the document concerned and that nothing else could have been intended than the proposed rectification.” In practice, this narrow definition usually restricts granted requests to those which seek to remedy misspellings and other typographical errors.
Article 19−Amendment of the Claims Before the International Bureau
When it is necessary to correct an error within the claims an applicant may refer to Article 19. Under Article 19, within 16 months from the priority date of the PCT application or within 2 months from the mailing date of the International Search Report and Written Opinion (whichever is later) the applicant may file a request with the International Bureau to amend the original claims. Said request should consist of a cover letter explaining the necessity of the amendment, a set of replacement claims and a statement under Article 19.
It is important to note that an applicant cannot utilize Article 19 to request an amendment to existing claims in situations where the International Search Authority has indicated that no International Search Report will be established.
Article 34−Procedure Before the International Preliminary Examining Authority
When it is necessary to correct an error within the specification, claims or drawings, an applicant may refer to Article 34. Under Article 34, within 22 months from the priority date of the PCT application or within 3 months from the mailing date of the Search Report (whichever is later) the applicant may file a Demand for International Preliminary Examination, a response to the Written Opinion and replacement sheets for any amended aspects to the claims, specification and/or drawings.
It is important to note that an applicant can also utilize Article 34 to present arguments as to the patentability of the claims.
National Stage Entry
If an applicant cannot take advantage of Rule 91, Article 19 or Article 34 to affect desired changes to the filed PCT application they have one last opportunity−national stage entry. This is, perhaps, both the least desirable and most expensive route as it requires the applicant to address the requested changes with each country at the time of national stage entry.