Why does my milk bottle lid have two dates
I haven't been across the border in a while, but I just double-checked via image search.

Most dairy products (and other foods with a short shelf life) in Switzerland have or had two dates, a "sell-by" and a "best before" or "consume by" date. 

Often, there will be a descriptive text, sometimes even in German, French and Italian, but there are brands that omit the text, probably because the average Swiss consumer knows how to interpret the double dates.

An example of a non-dairy product is this:


Source

Interestingly, there was a debate about the double date, centered around the confusion of consumers and their impact on food waste. Some supermarket chains like Coop have removed the "sell by" date since 2016, Migros insists on keeping it. (Source, in German)