No errors are acceptable, period.
If I were to write out three paragraphs of text on here, I would check each paragraph for errors until I was satisfied they were all correct before I clicked the 'Post Your Answer' button. If I found errors, I would not be satisfied with what I'd written until it was correct.
Why would a 400 page book be any different? As far as I'm concerned it isn't.
However, living in the real world and being the pragmatists we are sometimes compromises need (and have) to be made.
How much money are you prepared to spend on proof reading those 400 pages over and over and over and over again to ensure there isn't one single error left? Because you can do that if that's what you're prepared to do. However, for most people, business people, writers, publishers etc that simply isn't financially viable.
You have to draw a line somewhere and accept that given your budget for publishing that 400 page book you cannot spend all your money on proofreading and for the project to be financially viable you will have to accept that some errors will slip through the net.
So what it really comes down to is a cost v error acceptability rate. What that rate will be will almost always come down to how much money you're prepared to spend on it and the quality of the people you spend it on.
You're 'worried you haven't done your job', as far as I'm concerned just getting the 400 page book published means you've 'done your job'! If it contains any errors, log them and correct them on the next reprint!