The questions that serve as "concealed control" questions in the General Question Test are commonly used as sacrifice relevant questions in probable-lie "control" question "tests" such as those commonly used for pre-employment screening. It is not surprising that you would have encountered such question in your recent polygraph examination.

George:

I am living proof that they are still using this concealed control question!

The "concealed control" questions described on p. 89 of the 2nd edition of The Lie Behind the Lie Detector are part of a technique known as the General Question Test (GQT). It appears that the GQT technique has been largely discontinued. The GQT would be recognizable by the fact that, except for the "concealed control" questions, it otherwise outwardly appears to be a relevant/irrelevant format.

I think that the function of the "symptomatic questions" is adequately described at p. 91 of the 2nd  edition. You might care to re-read it. There is little need to augment reactions to such questions, though doing so might not hurt, either.

Appendix A lists versions of the MGQT. Specifically, Question 9 (of the FBI version) asks "are you lying to me about anything..." THIS IS A RELEVANT QUESTION.

However, on p. 89, it lists two concealed control questions. The latter one, "Have you lied to me, or have all of your answers been truthful, etc..." seems to be very similar to Appendix A's relevant question.

How can one distinguish between these two?

Gosh, it really seems like if you artificially raised your physiological responses to any of those "control" questions, it seems like an examiner would infer that you are deceptive.
 

Lastly, p. 91 talks about Symptomatic Questions. Any use of CMs here? What are their real importance?