Hi David,
I’m not sure I can shed too much light on your questions, but I had a potter around my book collection. There’s a good discussion of “The Julian and Gregorian calendars” in section 1.10 of “Historical Eclipses and the Earth’s Rotation” by F Richard Stephenson. (Contact me off list if you’d like a photocopy of the relevant pages) I get the impression that Scaliger’s work was part of the concerted efforts around the reformation of the calendar in the late C16. But I’m not an expert (just the Historical Section director).
Mike Frost