I looked up the article on Newspapers.com after Ed posted it, to see if there were others like it. (I didn't see other articles explicitly mentioning gambling, but did not look too deeply) I posted that article snippet with the full citation in the "Archive" section for that "Sloppy Joes" listing. I will let the Cuba experts use it as they see fit.

For unlicensed establishments (illegals so to speak), newspaper articles like this are probably the most important source of evidence.

For the California ChipGuide, I have been uploading 100s of old news articles into the "Archive" section of listings. I do this especially to provide supporting evidence to document that gambling took place there, dates of operation, ownership, etc.