On the other side, I've also noticed it appears to be aggressively pruning its index in the past few years, so the fact that it's crawled your site doesn't mean it's necessarily searchable either.
Another "bug" that seems to manifest quite often: if I search for a specific phrase or unique word on a page that I found in a SERP, so I know it's crawled that page, it often doesn't return that page either.
Add to that the automatic CAPTCHA-hellban you get if you use "site:" in anything more than a tiny amount (and the one you still get if you search "too much"), and I realise that there's increasingly huge amounts of information out there on sites that Google may have crawled before and knows about, but doesn't want to show me for some reason. I remember it used to be much easier to find information about obscure topics even if it meant wading through dozens of pages of SEO spam; now it's nearly impossible for anything but the most vapid of queries.
Another "bug" that seems to manifest quite often: if I search for a specific phrase or unique word on a page that I found in a SERP, so I know it's crawled that page, it often doesn't return that page either.
Add to that the automatic CAPTCHA-hellban you get if you use "site:" in anything more than a tiny amount (and the one you still get if you search "too much"), and I realise that there's increasingly huge amounts of information out there on sites that Google may have crawled before and knows about, but doesn't want to show me for some reason. I remember it used to be much easier to find information about obscure topics even if it meant wading through dozens of pages of SEO spam; now it's nearly impossible for anything but the most vapid of queries.