There are complex laws governing residency which vary country-by-country. It's not atypical that, for example, if you spend 183 days in a year somewhere else, you're no longer a resident.
You're generally only a resident in one country. This governs taxation -- taxes are primarily based on residency, with some caveats. As a US citizen living in the EU, you will not pay the same US taxes as you would if you were living in the US, and in many cases, zero taxes.
to change your status of residency, proof would be required.
and it depends who is asking. maybe i don't pay taxes as a resident, but for visa purposes i may still count as resident in my home country.
this is relevant now as china allows people only to enter by direct flight from their home country or country of residence. this is really messing with people who have their family in a third country. they have to make a detour to their home country if they don't have a residency visa for their family's country.
also if i go travelling for a year, i don't loose my residency status unless i stay somewhere long enough to establish residency there. that is, if i have a visa that allows that.
If you've lied, there are periodic audits, and you might get thrown in prison.
I assume you can lie going to China. If you do and get caught, you'll probably never be welcome to visit China again (or fines, or prison, or some other consequence; but most countries would just keep you out).
However, as the other poster pointed out, from the perspective of a tech vendor, understanding the difference between:
- EU resident
- EU resident using a VPN in the US
- EU resident traveling in the US
- EU non-resident living in the US
For each request which comes in is practically intractable.
GDPR is also framed as a basic, universal human rights law. That also can have unintended tentacles. If you don't want a liability hole, it makes sense to honor GDPR for everyone, in practice (even if not under your ToS).
Practically, that's what everyone does. I've never had a GDPR request declined on the basis of residency (the last qualification being important).
