web_speed... fascinating. Some brief notes for now, as it's late, and I don't want to take this discussion too far off the topic of serp updates. I think you are onto something worth exploring, and I do have some thoughts about where to discuss it if I can catch up with my own work. This is potentially a very long discussion.
But, let me emphasize that I don't think it's Google being duplicitous. Google simply doesn't have the data, and from the checking I've done, I'd bet the data is rare to non-existent. Eg, neither knoxfield nor knoxfiled shows up in a database of the top 25,000 places in the US as sorted by population, and I couldn't determine population for them anywhere on the web.
But NO, Google insisted on presenting nothing but results for "knoxville" with the "did you mean" link nowhere to be seen.
That's how all the engines I tried react to queries that include these placenames, and I tried a bunch. To oversimplify what I saw, just about every search involving either "knoxfiled" or "knoxfield" reverted to "knoxville".
Google occasionally returned knoxfield, depending on what the TRADE_PERSON or widget search for was, but on many of the searches I tried, there was no "did you mean" link because there were no matches for the queries.
It's possible that Google, as you say, is switching databases and they may have data satisfying the queries somewhere, but I have a very strong feeling that there isn't much. I have seen, during an update process, scanty data disappear for a while and then come back. As I understand it, that's the way a very large set of interconnected database systems has got to work. There's necessarily a degree of latency, and the tradeoff for speed is temporarily dropped data.
Also, on all the engines I tried, and I tried a bunch, every
search for knoxfiled tn
reverts to knoxville tn
For "knoxfield tn" in quotes, Google showed only 2 results (and one of those is like a wildcard site and nothing's there)... and for [knoxfiled tn], without quotes, Google showed only 8 results. None of the other engines showed any results at all.
Also, when I tried to set location, which is a fairly dependable way of observing US geo-effects on Google, knoxfiled, tn and knoxfield, tn both tripped a "location not recognized"
message in red. Of those we're discussing, Knoxville was the only location recognized in the location setting. Conceivably, Google is working off a variant of a placename database that's commonly used, and those names aren't there, and there are some good reasons why they might not be.
Rough observations about the ads... they appear to be tripped by a combination of keywords and IP location... I'm not an AdWorda person, but I know you can target AdWords locally by IP... so for certain trade_person queries, if I used my own default location, I'd get what appeared to be national trade_person directories targeting, say, a zip code radius... just a guess. So, if Knoxfile is near you, possibly you'd get a local ad even though there are no listings in organic. How large is Knoxfile, and is it an incorporated town, a suburb, or an unincorporated region?
I see that scottsonline is posting on this thread. He and I went through a discussion of a similar rare query search, involving also Google Suggest, autocomplete, spelling correction and query rewriting, and results not appearing that for content we saw was indexed. This was back in June and July 2010, as Caffeine was with us. See these threads... A Red "Did you mean: ____" Shows in Google Drop Down Suggestion http://www.webmasterworld.com/google/4178034.htm
[webmasterworld.com] 2:Google Updates and SERP Changes - June 2010 - - Clickable link would break in WebmasterWorld redirect script in this url:
Among other things, the discussions make clear why we don't want to use too many specifics here, as we end up greatly distorting the results.