What exactly do the three "special locales" called "en_US_POSIX", "en_001" and "en_150" mean?

There are quite a few English-language locales on my computer system (Windows 10). Most of them look like this, and make sense:

en_CA
en_DE
en_GB
en_IL
en_PK
en_US
...

But there are three special ones, which don't seem to correspond to a clear physical area:

en_001
en_150
en_US_POSIX

By doing some digging, I have extracted out the following "display names" for them (in order):

World
Europe
United States

Okay, so "001" means "World", "150" means "Europe" and "US_POSIX" means "United States", just as "en_US" already does?

What is the point of the duplicate "en_US" locales, and what is "World" and "Europe"?

It should be noted that numbers seem to be formatted just like in the US variants for both "World" and "Europe", which is unexpected. I thought they were gonna be using spaces for thousands delimiters, as I thought was considered the "international" standard, but they use commas, just like in the USA/UK:

123,456,789

001 and 150 are UN M.49 codes for "the world" and "Europe" respectively.

en_US_POSIX was invented to refer to the C (or 'null') locale code used in POSIX libraries. It's basically American English, with some peculiarities.

Note that this last one is under heavy discussion at this instant.