Hi..
Apart from the document no. and version number, and the general font readability, and graphics, we check for the presence of all pages and sequence, as its a booklet. Since our IFU are also size controlled, to seat in specific location within the packaging, we check for this L x W too with a simple cutout fixture.
Typical problems we have seen are Size big or small, some pages printed matter is cut in the final trimming, missing pages, repeat pages, wrong sequence of pages, Ink smudge between pages.
As some of the IFU are perfect binded, we also check if any pages are not glued OR extra glue has stuck few pages.