Louis Riel in Lonely on the Mountain is a mistake that was clearly obvious, so it's a good example. It was also written after he got a bit more serious about the era of his stories, so it sticks out.

Again dealing with the practical aspects of writing: until the mid 1970s we had a solidly middle-class lifestyle if Dad wrote 4 books a year. No private schools. One car. One TV. One phone line. Typical of that era yet kind of minimalist when you think of a quite successful writer today. Dad didn't get 4 books written by spending a lot of his time mired down in double checking details. He wrote. He moved on.

Of more general note: "Westerns" until the 1970s were darn near always set in that "generic western period" of 1865 to 1890. That's how you knew it was a western. Sometimes writers would pretend that period somehow lasted longer, sometimes setting multigenerational stories in that 25 year window. Dad was one of the writers who worked to break people's expectations that "all westerns would be the same" ... but he also played the game when he wasn't specifically trying to break the rules by branching out to other time periods. The typical western from before 1970 existed in a special universe where "the west" was separate from the historical flow of time and from the rest of the world. That concept bugged Dad but that doesn't mean he was trying to fight it with every story he wrote.

The first few Sackett stories (meaning starting with the Daybreakers) are quite carefully set out in time. Then he stopped calling attention to it. He MAY have realized that he was crowding era with stories that might start to overlap. Lonely on the Mountain contained the reference to Riel because he was interested in Riel. He probably forgot the fact that it overlapped or he thought it didn't matter. When he wanted to believe it was all one perfect continuum then that's what he believed ... when he wanted to make an exception to it, well it was his imaginary universe.

You know my opinion: if you sweat it, you are complicating the entertainment experience for yourself. But I'll also say this: If you sweat the "everything single LL said about history is perfect and everything he said about the landscape is there" aspects it will lead to disappointment. He liked to be right but he wasn't going to let it slow him down when he was writing and if reality conflicted with entertainment he allowed himself to choose entertainment if he needed to. There's a term used in the fiction business: "Willing suspension of disbelief" ... basically, a writer owes it to his audience to offer enough "reality" so that they don't waste energy on picking out erroneous details. It means make it believable enough so that the audience can relax and enjoy. That's what Dad did. Accuracy was a trend not a crusade. Occasionally he spoke about it as if it was a crusade but in those instances he was doing himself a disservice. It's always better to under promise and then over deliver.