One can answer the census questions anytime, but the status of the answer must be as of April 1.

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April 1 provides the official reference day for the decennial census, meaning that households are asked to answer the questions as of April 1. For example, on the 2010 Census form, the first question asked, “How many people were living or staying in this house, apartment, or mobile home on April 1, 2010?”
https://www.baltimoresun.com/news/maryland/bs-md-census-day-...

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Note added at 5 hrs (2019-04-07 13:47:07 GMT)
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opcja,
oficjalna data, do której odpowiedź się odnosi

No joke: It may be called Census Day, but April 1 isn’t actually the day the Census Bureau will start mailing out its 2020 census forms. That would be March 12.

Nor is it the day your census form is “due” (sorry, Jon Stewart). The final reminder postcard is set to go out in late April 2020, with in-person follow-up interviews to be conducted through July.


So what is April 1, 2020? Here’s the answer, along with a few other other things you might want to know about our once-in-a-decade population count in 2020.

Why is April 1 Census Day?
April 1 provides the official reference day for the decennial census, meaning that households are asked to answer the questions as of April 1. For example, on the 2010 Census form, the first question asked, “How many people were living or staying in this house, apartment, or mobile home on April 1, 2010?”

Why use April Fools’ Day as the reference day and not, say, New Year’s Day? The decision was made in 1930, prompted by difficulties 1920 census-takers faced during the winter months.

https://www.baltimoresun.com/news/maryland/bs-md-census-day-...

Dzień referencyjny – ogólnie pojęcie to oznacza datę, do której odnoszą się dane dotyczące jakiegoś działania.

https://forsal.pl/finansopedia/gielda/hasla/912006,dzien-ref...

ROZDZIAŁ 2
SPRAWOZDAWCZE DNI ODNIESIENIA I DNI PRZEPŁYWÓW GOTÓWKOWYCH ORAZ PROGI SPRAWOZDAWCZOŚCI
Artykuł 2
Sprawozdawcze dni odniesienia
1. Instytucje przedstawiają właściwym organom bieżące informacje w następujących sprawozdawczych dniach odniesienia:

https://eur-lex.europa.eu/legal-content/PL/TXT/PDF/?uri=CELE...

CHAPTER 2
REPORTING REFERENCE AND REMITTANCE DATES AND REPORTING THRESHOLDS
Article 2
Reporting reference dates
1. Institutions shall submit information to competent authorities as it stands on the following reporting reference
dates:

https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELE...

https://iate.europa.eu/search/standard/result/1554739487316/...