The Red Axe (1898) and Joan of the Sword Hand (1900) are both set in fictional Baltic German states and real Hanseatic cities in the 16C. It's clear Crockett doesn't know or doesn't care about Salic Law, because he has sovereign princesses in two of his principalities. The time-period is fuzzy, not helped by the illustrator, Frank Richards, who draws male characters in 16-early 17C costume, and the women (at times) in more 15C dress; but there are references to muskets and cannon, to farthingales, and the coranto, all of which clearly indicate a 16C setting. In Joan (and why Anglicise her name?!), there are references to a Pope Sixtus and a Prince Ivan of Muscovy, which only confuse things further. (Sixtus IV r. 1471–1484; Sixtus V r. 1585–1590; the former was contemporary with Ivan III, but the latter was just after the death of Ivan IV.) There seems to be no mention of the Reformation, which seems bizarre, as it would have made sense as a factor in the dynastic conflicts which take place.
But what really galls with Crockett is his attitude towards women. Hope idealises Flavia, but in The Red Axe, Helene is referred to as "The Little Playmate" by the hero, even when she is a grown woman, and is horribly sentimentalised. Also, in Crockett's hands, Antoinette would never have been allowed to reach the end of PofZ breathing. He is of the "the Fallen Woman must die a redemptive death" school of Victorian novelists. I was highly annoyed that the femme fatale Ysolinde von Sturm – far more interesting than Helene – had her cleavage rearranged with a lance or pike in The Red Axe. She's a woman who could have scared the wits out of Rupert! I suspect Crockett had problems with the 'New Woman' of his own time.