As communicated earlier, the PCT requires applicants to indicate a basis for amendments. The September 2010 PCT Newsletter provides a few examples of how applicants can, in their letters, indicate a basis for amendments.
The PCT Newsletter states,"the letter must make specific references to particular parts of the description or the drawings." The Newsletter also states, "non-specific indications such as 'see the description as filed' or 'see the claims as filed' are generally not considered sufficient for an indication of the basis for the amendment." The full newsletter can be found here.