Yes, and they don't just hand you an FASG. But when you manage a project of that size, you either end up relying on others or doing more than is humanly possible. So it is hard to let mistakes creep in. That's partly why I asked specifically about smaller articles, that should be easier to get close to perfect.
I tracked down the quote I had read, which came from a state historian of part of the GSMD, so I guess not an official representative of the organization, but still probably knows a thing or two:
The interesting bits describe how in the early days of the Silver Book project, "the Howlands insisted that THEY would do Howland; it was envisioned as a 10 volume set, to be published by Picton Press... Elizabeth Pearson White, compiler, got the first two books: DESIRE and JOHN, done, fairly well, but then she produced NOTHING more for years. In the early 2000s the GSMD informed the Howlands that since they had not produced any more volumes, the GSMD would have to take Howland over. At that point Ms. White said she had HOPE and ELIZABETH close to being done, and it was agreed that she would finish those (thought they are not up to the standards met in Desire and John) ... these later two books have many more mistakes in them than the first two books."
I had looked in the Hope volume for the ancestor I mentioned, so it looks like I would have been better off if I descended from Desire or John. It also sounds like White was running this completely by herself. If so, then it is not surprising that with such a large project, and time pressure, that mistakes would enter.