First of all, thank you for testing "dcmrt" and for your comments.
With regard to the missing attributes: You might have realized that more than 99% of the classes (including their implementation) are generated automatically from a machine-readable version of the DICOM standard. The comment header of these source files contains the following line:
Generated automatically from DICOM PS 3.3-2007
That means the 2007 edition of the DICOM standard has been used for this purposes and this version did not yet contain these attributes. As soon as there is a more recent machine-readable version of the DICOM standard, we'll use that and regenerate the classes - which is just a matter of some seconds
However, I guess you're right regarding CumulativeDoseReferenceCoefficient - I'll check that ...
With regard to your suggestion: The other elements can be accessed directly via the dcmdata API using the dataset that is passed to the read() or write() method.