It’s often annoying, especially in a moderately-sized site, to find that some pages aren’t appearing in the Google search results. We might reasonably ask ourselves if this is a problem at our end. It may be, but more likely because our site isn’t regarded as being of particularly high quality, according to a recent Google SEO ‘hangout’.
It’s apparently quite normal for indexation not to be comprehensive – “it’s always going to be the case that we don’t index 100% of everything that we know about”, says Google. The higher quality the site, the higher proportion of pages that are likely to appear in the results.
However, don’t confuse this with site crawling – all but the largest catalogue sites will get most or all of their pages crawled. Google’s been there, even if it’s not showing everything in the results.
My suggestion for pages which Google doesn’t seem to be acknowledging is to get some decent external links to them.