Yeah, significant bit in my explanation shouldn’t be confused for endianness, that works like you explained. But I’m still of the opinion that iso8601 is best saved for when you need to save dates/datetimes or when confusion can occur. Human-to-human communication is more often than not informal and redundant information can be left out more often and that is where the significance of the bits comes in. Maybe I should have called it the importance of the parts to avoid confusion.

But save to say, I use iso8601 most often anyway. Who is communicating with other humans nowadays?