Liz Burns has a Shelf Space/Foreward piece on ARCS. I quote:
"Fantasy author Sarah Prineas illustrates how the difference between an ARC can be more than a misspelled word: "the ARC quite often is an earlier iteration of the book, so might contain a lot of sentence level and continuity errors and infelicities of prose that will be caught in a later copy edit. Another difference is that if a book has internal illustrations, these will often be either missing from the ARC or present only as rough sketches.""
This, people, is why librarians absolutely should not shelve ARCs in their collections. If the book is in ARC form, it's not done!
Liz will have more to say on this subject next week.