Your NGram query appears to be case-sensitive (the "case-insensitive" option is not active). And there is a sudden rise of the (lower-case!) "uk" starting somewhere between 1990 and 2000. And the the TLD of British websites, such as British editors, is .uk. Hmmmm. Coincidence?

"Professions without further qualification" - even this is misleading. "Er arbeitet als leitender Kellner." is fine, as "leitend" is a part of the job title here, even though structurally, it looks the same as the qualification "erfahren".

@vectory: Nein, es heißt Symphonie oder alternativ Sinfonie.

In the first sentence, do you actually mean "comma", or rather "colon"?

"Sümpfe" und "Symphonien" sind ein weiteres Paar, wo man den Klang gut vergleichen kann (und vermutlich keinen erkennen wird).

Nice hypothesis concerning asking for yourself vs. someone else - but does anyone actually use the words like that?

Verstehe. Ich las das als "man könnte" = "andere, ggf. der OP, machen es vielleicht, aber ich empfehle, eher zu überlegen, wieso die Korrektur vielleicht doch berechtigt ist".

Ich glaube nicht, dass "Das ist mir egal." die Antwort des OP auf die Korrektur war, sondern ein Beispiel, in dem der Dativ verwendet wurde.

'"Trümmer" meaning "ruins", since there are archaic singular forms' - that was very surprising to me, but common online dictionaries confirm your statement. In spoken German, I would without any hesitation say something like "Da liegt noch ein Trümmer herum.", and I am sure I have often said and heard others use this singular form.

My impression is that none of the examples in either reference that is chosen to show the meaning "occasionally" is very clear-cut. Often, the fact that something happens occasionally precludes that it is a permanent thing, and therefore implies that whatever happens does so temporarily (if multiple times). As such, in most, if not all, of the examples provided, one could argue that "zeitweise" does mean "for a while", "temporary", "for a limited amount of time", or at least emphasize that aspect rather than focusing on the occasional reoccurrence of the event.

I am not sure "Das wird schon werden." is another example along the same lines. "Das wird schon werden." is indeed about a future event, so it is a spot-on use of future tense in its original sense, unlike the use of an assumption (where the future aspect is maybe only meant to denote the speaker will learn about the fact only in the future).

... aber eben nicht in der Annahme, dass es tatsächlich Vettern sind, die diese in einem konkreten Fall betreiben.

@bakunin: "ich denke, wenn man bei Berufsbezeichnungen das grammatikalische Genus dem biologischen Sexus unterordnet, dann sollte man das auch bei Verbrechenstatbeständen tun" - bei auf die Personen bezogenen Begriffen stimme ich dir ja zu, nur bezeichnet "Vettern" in "Vetternwirtschaft" ja gar nicht die Personen, um die es geht. Insofern stimme ich auch der Aussage aus der Antwort hier, dass "niemand (...) an Vettern (...) denkt", nicht so ganz zu - doch, man denkt an Vettern, weil Vetternwirtschaft ein Verhalten ist, wie es vielleicht unter eng vertrauten Vettern zu Tage tritt, ...

Another data point: Some 30 years ago, when I was still in school, it would have been totally unthinkable for my parents to adress any other parents of my classmates/friends with "du", or with anything other than "Frau/Herr <surname>". Nowadays that my own kids are in school/child nursery, it has become entirely natural without any exception that parents address each other with "du" and the first name. Just the teacher/child nursery educators are addressed with "Sie" by us.