If they do, in many of those countries you will likely become a very rich man. So long as you did your part by answering the questions on the relevant medical honestly.

You are required to answer questions honestly and submit to a medical examination. So I am assuming this scenario would apply to a condition which might decertify you under CAD rules yet permit certification in the other country.

Most real nations have fairly strong health privacy laws. Breach of these is always a civil and sometimes a criminal offense. There might be some limited cross flow allowed when it can be demonstrated there is a bona-fide and imminent threat to the safety of self or others. But disclosure of protected information is an absolute minefield for a company in some developed nations.

You will have to report your loss of medical when you take a medical in your original country :)
Have you ever been refused a medical question on the class one application.

I believe someone lost their class 1 in the UK unexpectedly and was informed that they would be notifying the HKCAD as it was required, perhaps not the reason for the loss but that they could no longer hold a class 1. I assume it was on record that the person held a UK and HK class 1.

That is not correct and it depends on the jurisdiction. Some require you to report the loss of any medical, some only want you to report the loss of THEIR medical in that particular country.

Of course, the condition which caused the original loss of medical would have to be reported regardless if it met the criteria of questions in the place it was applied for.