One of the most important aids was Martin Wiggins' magisterial catalogue British Drama, 1533-1642, the relevant volume of which was published in 2013. It includes a detailed entry on every play of the period, including the lost ones. The 'Wiggilogue' is an extraordinary achievement, and my copy of volume 3 is now thoroughly battered and coffee-stained.
Also invaluable has been the burgeoning field of 'repertory study', which investigates the careers of individual playing companies and treats their plays as a body of work, much as a more traditional study might group plays according to their author. In the early days of the blog, I was using Lawrence Manley's and Sally-Beth Maclean's Lord Strange's Men and their Plays (2014), and in the latter stages two books about the Admiral's Men: Andrew Gurr's Shakespeare's Opposites (2009) and Tom Rutter's Shakespeare and the Admiral's Men (2017). Laurie Johnson's Shakespeare's Lost Playhouse (2018) wasn't published at a time when I could use it, but it's a brilliant study of the period in which Henslowe's Diary records performances at the Newington Butts playhouse.
And of course, there are the scholars who have worked to understand and explicate the huge and baffling document that is Henslowe's Diary. The standard editions are R.A. Foakes's (2002) and the online facsimile at the Henslowe-Alleyn Digitization Project. But they were built on the foundations of work by Edmund Malone in the 18th century, the complicated John Payne Collier in the 19th, and W.W. Greg in the early 20th. I also found extremely useful Carol Rutter's Documents of the Rose Playhouse (1984) and Neil Carson's Companion to Henslowe's Diary (1988).
There is much more to learn about this fascinating document, as you can see, and we owe a great debt to the work of these heroes of scholarship.