How long is a history book?

Long time coming

In a reminiscence of the historian Michael S. Cross (1938-2019), who died in Halifax in September, his student and colleague Peter Twohig recalls attending a presentation by Cross in 1983 when it was mentioned that Cross was working on a biography of Robert Baldwin.

Well, he was. The book was published in 2012.

So, a good thirty years at least. Now, Twohig's appreciation and this one from Dalhousie history department, each remind us that Cross published a lot else and did a lot else in his professional career.  I mean no disrespect here, and the Baldwin book is pretty good. (Thirty years good, though?)

Anyway, it makes me wonder what the record is for the gestation periods of Canadian history books. Anyone have comparable examples?  (There is this one, but in this case the eventually published book was not "in progress" the whole time.)