I have written new NDR-checking code for CCTS models and I applied it against the UBL 2.1 model. This revealed three issues to be addressed in the next revision of UBL: removing sensitive XML characters from documentation, removing an unused ABIE from the library (assuming no third party is using the library), and changing the cardinality of one ASBIE to be optional and repeated instead of mandatory and repeated. All of these changes are backward-compatible with UBL 2.1 in that all possible UBL 2.1 instances will validate with new schemas that incorporate these three changes.
What follows is an excerpt of the report and it highlights the three issues (I'm not sure how they will be presented in JIRA).
. . . . . . . . Ken
COM02 - prohibited characters: 58
(a list of 58 BIEs with the business process documented as "Marketing & sales)
Orphaned ABIEs not being referenced by an ASBIE: 1
"Performance Data Line. Details"
Missing expected BIEs in Document ABIE: 1
Guarantee Certificate. Signature: Signature (expected cardinality '0..n',found cardinality '1..n')