You are trying to apply what you know versus what others know. No different than Farenheit vs Celsius or Yard vs Meter.

Personal, the MM/DD/YYYY format, that is stander in the USA, needs to die and be replaced with YYYY-MM-DD.

Same with 12 hour time and replacing it with 24 hour. As the saying goes l, Americans use am and pm because they can't count past 12. AM and PM are a waste of code and display area. What fits in 2 characters takes up 5 characters.

It depends on the local norms. Where I live, 1,004 is decimal, 1 004 or 1'004 is 1004 which makes it even more clear than the en-US default. That is, the 1.004 variant is never used, and if it is, it is assumed to be a decimal (misspelling) of 1,004.

You don't. It's ambiguous. Just like the string 01/03/2025 is if you don't know the source's locale.

But it can be worse. Los Angeles, Sunday, November 2, 2025, 2:00:00 am is ambiguous. Is it PST or PDT?

What I used to do is set the thousands separator to ' in the operating system settings. That made Excel read CSV files with 1,004 and 1.004 the same, as one and four thousands. No one puts thousands separators in CSV files anyway, so that worked out. And it looked nice too.

In today's Windows 11 I can't find that setting. You can't set the thousands separator separately, not anywhere that I can find. It's a tragedy. I see Excel misreading CSV files all the time. I don't use Excel that much myself and I understand what's going on, so it doesn't affect me all that much directly, but for my Excel warrior colleagues, it's another matter.

How do people who use periods disambiguate it? It’s simply ambiguous without context.

I mean, if that's how you write numbers, it's the same as disambiguating 1,004 and 1.004 if you use EN-us norms.

Which is to say, you assume it's as written, unless context suggests otherwise.

The same way as people who use periods. 1,004.004