I'm not sure if I agree with that.

> Describe the events up to WWII

For me that sounds like you would include WWII, just like if you counted up to 20.

> Describe the events leading up to WWII

Then I would agree, that would be "explain the set of events on which WWII depended" so that would include all prior events which are relevant to WWII, without including WWII itself, but also missing out any events not relevant to WWII, so not e.g. "OK so the ice age was before WWII, so let's start there".

(Native English speaker, from UK).

In my experience, spoken English is relatively fault tolerant, which probably makes speaking it less challenging than it first appears. To become proficient, you slowly learn the rules.

Not sure how this compares to other languages. I’ve only observed other people learning the language. As a typical American, I only speak American English. If you mentioned the boot of a car, I’d probably ask if you meant the tires. ;)

I think the difference in this case is that we naturally parenthesize the sentences differently:

(Count up) to 20.

and

Describe the events (up to) WWII.

Because "count up" and "count down" have precedence over "up to" in the linguistic order of operations, so to speak. There's of course no "describe up" or "events up", so "up to" has precedence in the second case.