Google have changed they way they are reporting site crawls.
Pages that don’t update, i.e. those pages that present a 304 (Not-Modified) response to a If-Modified-Since qualified request, Goolle will provide the date of that request.
“We’ve recently changed the date we show for the cached page to reflect when Googlebot last accessed it (whether the page had changed or not). This should make it easier for you to determine the most recent date Googlebot visited the page“
It would be extra-good if they’d advise more details on when new crawled pages are included in the index, and if not, why not 😉