OP this is a very good topic but maybe you should add exact License information for each casino, and I know that most of them are using one of Curacao licenses but some use different.
One example I know is BTC365 website that is using E-Gambling Montenegro gambling license, but there are others who use license from Costa Rica.
As for Costa Rica, as far as I know, there is no such thing as a gambling license in this country. Apparently, when registering a company, it is enough to specify "gambling" as the purpose of the business and it is enough to be able to legally run a casino there.