Now that the IATI Standard is stable, please consider the option of including the most of the codelists in the Schema. In my opinion, all of them should be.
So, it would be possible to identify erroneous codes when the XML file were validated against the Schema and before uploading in the IATI Registry.
There are several technical solutions in the Schema definition languages to solve it. From the basic option of using the "enumeration" constraints inside the Schema File to the complex "Context/Value Associations".
I think that, at least the first one, would increase considerably the data quality.