Research is a tricky thing. How much is not enough? How much is too much? Is it the world's best writing procrastination tool? After all, if you're doing research you are working on your novel, right? Yeah, but you're not actually writing it. My students often ask me if they can submit the number of words they've written down during research as part of their novel writing word counts, and I'll inevitably say no.
Do we expect writers to know everything? Is it even possible? And do we expect editors to pick up every little mistake that's slipped through. Think about the reader though -- is it average Joe or someone with specialist knowledge?
A few years ago I was listening to a well-known editor from a well-known publishing house, talking about a well-known author's well-known book in which the sun magically set in the east. Three editors had perused the copy and not one of them picked it up. Readers did though. And complained.
I also remember reading another well-known author's prize-winning book, in which the main character talked about the Morlocks in the War of the Worlds. Trouble was the bad guys in War of the Worlds were Martians; the Morlocks were in The Time Machine. Right author, wrong book. Trouble was the effect this had on me as a reader was to totally distrust the narrator -- after all, he had presented this as FACT, and I found I could no longer trust anything he told me. He wasn't supposed to be an unreliable narrator, so this totally wrecked my reading experience. That wasn't me being smart or mean, that was me losing trust in the author, whom I actually think is a wonderful author, otherwise, but there you go.
So do you crosscheck every fact? It's really not possible. You'd never get any writing done. I subscribe to the look-up-the-facts-that-you're-going-to-build-your-story-on-now theory, coupled with the if-you-come-across-something-you-need-to-look-up-in-the-middle-of-writing-plough-on stream. Bookmarking is a wonderful thing. With something like that, I'll usually type in three asterisks on either side, and then later search for three asterisks. Doesn't matter what it is, provided you've got something you can easily look up.
Sometimes, with historical fiction, there is the quandary of contradictory resources. It's not always possible to go back to primary sources, but really there's no reason these mightn't sometimes be contradictory as well. Facts are always open to interpretation. Ah, the joys of research.