That's easy enough to fake. How is US customs going to know when a German company's ship registered in the Philippines left a Chinese port?

Presumably by asking the Chinese authorities directly? We have near instantaneous global communication these days - that's how I'm conversing with you right now.

There's also AIS

https://www.marinetraffic.com/en/ais/home/

Of course enabled by the very tech you mention.

There is a pretty huge amount of ship and satellite tracking these days

You’d just lie about which ship it was on.

While it's still in the shipping container with a GPS tracker on it?

I've very briefly worked with a team that was responsible for satellites that track ships and their AIS data, including trying to identify ships spoofing AIS though various means. (It was civilian, a university group, but I'm sure states have similar and more)

Do you have a source for this? Because from my own experience, and from everything I can find online, this is not true.

Tariffs are based on date of entry: https://www.vedderprice.com/remember-basic-import-rules-when... (see 'Rule 2')