So, I've been going through my chapters, filling in square brackets and checking problems in the footnotes. One of the things I ran across to check up on is the fact that, in one paragraph, I refer to a particular law, but give it two different citations in two different footnotes. Strange. Especially since I knew this paragraph was one that I had originally used in an article I published a couple of years ago, and I checked all the citations before it went to press.
So, I went back to the law book to look it up, and found my problem. Let's pretend this particular law begins with the phrase "Ad astra per asperem." Turns out that I had indeed checked out the source and verified that the reference in question actually began with this phrase. The problem is, I didn't read further – I just trusted the citation that had gotten me there, and the quick check I made.
Apparently, this law code has TWO laws that begin "Ad astra per asperem," separated by about ten pages. And within the space of three sentences in my book MS, I managed to cite them both. I've corrected it now, but the older article is in print, with the error.
And, I would lighten up, but this particular law is a very well-known and important one. And I screwed it up in print.
The only comfort I have is that the scholar from whom I backtracked the original erroneous reference – someone much more established than I – made the same error, and is also in print as such. So, the responsibility lies partly with Established Scholar, but mostly it's my own fault for not doing a thorough enough reference check. And while this is embarrassing, at least it's a lesson I've learned with an early-career article, rather than a book.