Yes, that is the standard oil and gas industry definition of "tight-hole". Wells are almost always tight-holed during drilling by companies with shares that can be traded. And like you say:
Which happened with the 5 JDZ wells. It took a few months to hear the results.
Again, it is the standard definition used in the oil and gas industry. Everyone is free to make up their own definitions, but I use the ones that are used by the industry I am involved in.
No, the opposite is correct. Using the study by Wood Mackenzie, the global energy mining research and consultancy group , which analyzed the historic patterns and results of wells held as tight. It found 20% were discoveries, 80% not. So about 80% of long-term tight holes turn out to be dusters, and about 20% are discoveries being concealed for competitive reasons. (This was a limited study, so the percentages are not universal)
JDZ Block-1 results were announced in 2010. It was only tight-holed for a few months. Both ERHC and Sinopec announced that the well encountered gas. Had they not announced the results, it would be tight-hole status.