It's hard for me to add something to this …
However, I will do because that in itself does not qualify as a good answer.
The basic point is that solely a number of words is highly irrelevant for speaking and understanding a language fluently. It is, as the author of the blog post states, a lot more important to understand context, place unknown words into a context, infer them, and continue talking about the subject using the vocabulary you have. It is also (as is implied in your question) important to know which word 'sounds' right in a given context – for example the close but nowhere near identical sehen and schauen/gucken. And finally, German is one of the languages where you can be a lot more fluent with a smaller percentage of words, because we have so many regional synonyms. (Alster/Radler, Sonnabend/Samstag, (Dach-)Boden/Speicher, Schippe/Schaufel, Brötchen/Wecke/Schrippe/Semmel, Pfannkuchen/Eierkuchen/Omelett, Berliner/Pfannkuchen/Krapfen/Krebbel … See the Atlas der deutschen Alltagssprache for more details.)
Furthermore, you asked specifically about the office context. That makes your question even harder and more impossible to answer. Consider someone working in the finance office. They'll need to know a lot of words concerning taxing and financing, that someone doing human resources or business trip stuff doesn't need. Conversely, both of those departments have their own set of significant words. If your 'office job' includes calling customers and talking on the phone, your vocabulary will need to be larger still, because you need to again know those regional synonyms I touched earlier.
Likewise, to answer your final part, if there is any official list of words that one needs to know for any of those language levels that go further than the personal pronouns, articles and present tense forms of sein and haben, that list is probably bad and should be abolished immediately.
Trying to think of something equivalent to the Chinese menu test the author of the blog post talks about, one of my first ideas is a Schafkopf test, i.e. attempt to understand and explain phrases/words used in a typical four-player Schafkopf game (it's most played in political Bavaria as far as I know). Note that most Germans (90 %+) would fail this test, even if you explained the rules of Schafkopf beforehand. Want a try?
- Die mit dem Hund drauf
- Blau ist die Hoffnung
- Wenn's ginge
- Schellinsky war ein Pole
- Eichel fressen die Säue
Answers in the spoiler:
Mit der Schelln-Sau
Mit der blauen Sau (standarddeutsch grün)