If you are asking if there’s a general unspoken rule in US that everyone knows but you are not aware of - no, there isn’t one that I personally ever heard of.

If you are asking if there’s a general unspoken rule in US that everyone knows but you are not aware of - no, there isn’t one that I personally ever heard of. But it’s not exactly unexpected that you may need to negotiate something with your specific employer. It sucks tho.