One thing here - make sure that the census taker shows ID and is legit. You never know who is knocking on your door these days.
And, BTW, welcome to FR.
I didn’t send the second one in, since it did mention somewhere in the cover letter that you only need to submit it if you didn’t already submit the previous one. But I strongly suspect an attempt at double counting. This was at an NYC apartment that is a secondary/part-time residence for me, and in a neighborhood that is largely non-white and welfare-dependent. I really wonder if this double-mailing practice was prevalent in predominantly white (and Asian and Indian) suburbs where most people are self-sufficient.
Even if the double mailings were done everywhere, they’d still be much more likely to yield double counting in minority/welfare-heavy areas. When homes are occupied by various unrelated people, and many include illegal immigrants and/or people regularly engaged in criminal activity and/or people who are barely literate, threats of prosecution and in-person visit from government agents are likely to prompt recipients of such forms to fill them out (not necessarily accurately) and send them in, regardless of whether they know or suspect that someone else has already sent in a form for the same residence.
Re: “..............One thing here - make sure that the census taker shows ID and is legit. You never know who is knocking on your door these days.”
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That’s why we never open the door or even acknowledge the bell or someone knocking — we can see the people outside and if we don’t know ‘em, we keep quiet until they leave.