2.4 At an advanced stage of the proceedings 

When the applicant files an extensively revised request to replace the text of the application on the basis of which a patent could be granted, they must provide good reasons for proposing the changes only at this stage in the proceedings. This applies particularly in cases where the examining division has indicated that a version of the claims proposed by the applicant is grantable and that the applicant has only to bring the description into line with that version. Normally only those amendments which do not appreciably delay the preparations for grant of the patent will be admitted under Rule 137(3). To this end, the examining division carries out a prima facie analysis of the amendments to determine the amount of time their examination might require. It is this amount of time that determines whether the amendments are extensive. If the examining division comes to the conclusion that a request is prima facie not allowable, for example, because it introduces new deficiencies, they refuse the request under Rule 137(3).