People with complicated lives do not want to be asked a lot of questions. Some people are in the habit of conducting a police-style interrogation in order to find out all there is to know. This may be well meant and may even just be a way of sustaining conversation. But private people like to be private.
The person who does not want to be asked questions may be indicating that in due course, at the proper time, all will be revealed. At the moment the answer to a question could give a false impression. It is not necessarily a matter of wanting to be secretive for ever.

A person hearing code 12/8 may choose to think the person has much to hide and is dishonest. That is a risk the code user has to take. He or she may seek to explain in ordinary language why there is a reluctance to answer questions.

The code suggests a mutual abstinence from questioning. It would hardly be fair if one party was free to ask questions and the other party was not.

The code is a perfectly legitimate request. In a court of law the past criminality of the defendant cannot be revealed at the start of a case because it would prejudice the outcome.