(The country that claims me as its citizen is irrelevant, and obviously we are indeed discussing ISO's definition of a "week". )
The country is indeed irrelevant. The culture however is not: as I noted, this week ordinal definition is standard in europe, and the only people I've seen 1. not know about this definition of the week (and the concept of week-year) and 2. care enough to express any sort of surprise, have been american.
> we are indeed discussing ISO's definition of a "week".
The information in my comment was that this is the standard week in europe, any time somebody talks in weeks (which is common in many, many businesses, people'll tell you they'll do a job W23, or will ship your order W36), that's the one they're talking about.
If I say that 3am on Saturday is part of "Friday night", that's not very surprising.
If I say that 10pm on Monday is part of "Tuesday morning", that's quite surprising.
Each is independently 'surprising' in that it seems 'obviously wrong' without thinking about it.