The Stack Exchange Data Explorer is a very nice and useful tool, but it has one very large drawback: Beta sites are not included at all.
Excluding beta sites probably made a lot of sense when the beta phase was supposed to last only 90 days and when updates to the Data Explorer were performed manually. With sites staying in the beta phase for years now this exclusion doesn't seem justified to me anymore.
All publicly launched sites should be included in the Data Explorer, there are more beta sites than launched sites in existence right now and excluding them does not really make any sense anymore.