Thank you for all of these great links, Mia! You've given me much more to explore and consider.
Yes, that was my suspicion as well, that, as you say, the phrase "Licensed pursuant to Act of Parliament" pertains to the venue being allowed to stage performances. Copyright law, both its history and its scope, is a fascinating subject, as it's continually evolving to meet the advances of technology, especially now with some much digital content and virtual means of disseminating information.
That is interesting about the early restrictions imposed on spoken dramas and the direct effect of that being an abundance of musicals, burlettas, and non-drama productions. I'd wondered why there were quite so many and had put down to the appeal of upbeat, comical, or otherwise light entertainment to wide audiences. That historical fact really helps put this trend into context.
I will check out the Restoration/18th Century Literature and the Romantics and Victorians collections for more information. Thanks, again!