[tingletech]

Another wrinkle is that the copyright clock traditionally starts at the time a work is published. So, unpublished manuscripts are not necessarily in the public domain, even if they were written 100s of years ago. If these were the King's personal maps, and just now published, they might still be under copyright.

[monoideism]

> So, unpublished manuscripts are not necessarily in the public domain, even if they were written 100s of years ago.

This may well be the case in the UK, but this assertion would likely not apply in the US, for multiple reasons. For one thing, manuscripts that have been displayed in a museum would be counted as published. Also, in the US copyright expires 120 years following creation, at the very latest.

[zozbot234]

Some countries have a special copyright status for a 'first' publication of unpublished historical content, called editio princeps. But the conditions for that to apply are somewhat stringent; a widely-copied manuscript would be considered to have been 'published' for example. In the US, AIUI, copyright on an unpublished work would run out 120 years after creation.