Advocates like attorney's are officers of the court and will in breach of the oath taken when admitted to practise by the court. As I understand it the advocate presents the client's version within a legal context for the court to judge the thruthfulness (and other things such as relevance) of such version. The advocate therefore puts before the court the clients version, even if unlikely. Should the clients version however be so unlikely one expect the advocate to confront the client. If the client acknowledge that its version does not represent the truth the advocate would be in breach of his oath to present it to court knowing it is not the truth. In such case there can be no consequence for the advocate refusing to knowingly be party to misleading the court. If the client however insist that his version is the truth the advocate must present the case to the court. 
This is how I understand the issue.