One time I was in a final review meeting for a service manual with four engineers, the engineering manager, and the V.P. of engineering. We were there to do a final content check. Service manuals tend to be long, detailed, and schematic/block-diagram laden tombs designed to enable someone to perform maintenance on some gadget, engine, or cute little electronic device.
While the engineers discussed one of the schematics, I glanced down and..there it was. A typo in the third paragraph on the first page. Mind you, this document had been through seven previous meetings, multiple reviews by all present (one of whom prided himself on his ability to spot typos), and multiple proofings by yours truly. What was annoying to all of us was, after checking the original, that blessed typo had been there from the beginning and not one of us caught it.
In short, the human brain is very clever in that it will often interpret text to read what it thinks it should be, not what is actually there. So, don't lose heart, Wesley, but just assume that no document will ever be 100% free of error. With fiction, it's even worse because there you add in the grammatical errors with simple typos and punctuation goofs.
Whew, my own progress report - finally got through the Battle of Cambrai (WWI, November 1917). The AEF has arrived in France and I just have to wend my way through 1918 so I am a little over half-way through Book VI. Fortunately, most of the remaining chapters are in my head so things should flow a bit better through the remainder of the draft.