UPDATE ON PREVIOUS POST: I think I spoke too soon!
I've been updating one of my sites and, over three weeks ago, stuck up a kind of temporary version as a placeholder. All this time later, DDG is not finding anything at all. I've been to Yandex [who powers DDG's site search] and they're still only listing hits from the previous version of the site, which hasn't been online for a month.
That would be bad enough, but is compounded by the fact I've got a Webmaster account with Yandex, where my site[s] are already "registered" for crawling. I've re-submitted the site AND uploaded a Sitemap and, over a week later they've still not updated any of the results for that domain.
Meanwhile, Google had picked up every single page on the new temporary site less than 24 hours after I uploaded it –and that was without me doing anything to prompt a re-indexing at all.
It looks like, if I want to avoid Google, I'll have to check out some of the static indexers mentioned above. On this evidence, DuckDuckGo [and by extension] Yandex is completely useless on any site where the content is likely to be changing with any regularity.