DJClayworth's comment under this question seems very valid to me:

Can I suggest not giving dates as number/number/year as they mean different things in different parts of the world. Writing the month name avoids confusion.

Do we insist on that?

(I'd say yes, and I'm writing this as a question here so that we have a meta post to point to).

Added: Suggested course of action:

We edit them out if the date is ambiguous and we know (from context) which date it should be; optionally we leave a comment (pointing to this meta post). If we cannot resolve which date it is, we leave a comment asking them to write the dates in an unambiguous format (pointing to this meta post).

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    Writing out the month is unambiguous, and I'd say that using the ISO standard of yyyy-mm-dd is almost unambiguous. – Ward - Reinstate Monica Jun 28 '17 at 20:57
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    So long as common sense is applied: "Airport security has changed since 9/11" is fine. – Andrew Grimm Jun 29 '17 at 2:01
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    Not insisted upon, but can certainly see the benefit! – Mark Mayo Jun 29 '17 at 3:05
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    If there is only 1 date and both numbers are between 1-12, then I can't decide if it's dd/mm/yyyy or mm/dd/yyyy. Otherwise, not really a problem. (Also, Date format by Country - Wikipedia)... bonus: 2-digit year is more painful. – Andrew T. Jun 30 '17 at 14:34
  • Mandatory xkcd. – ugoren Jun 30 '17 at 22:18

I support the proposal, so that the recommended notation is

  • 6 December 2015 (GB)
  • December 6th, 2015 (US format) or
  • 2015-12-06 (ISO)

because the US slash notation 12/06/2015 is not well known internationally and the order clashes with other long used patterns like day - month - year. December 6th, 2015 can be immediately understood even by people who have day month year (like 6.12.2015 in German) notation.

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    Agree, but particularly support 2015-12-06. It makes it easier to compare dates. – ugoren Jun 30 '17 at 22:21
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    (OP) Disagree with that last one. Primary goal is removing ambiguity, not adhering to standards. – user40521 Jul 1 '17 at 10:13
  • @ThorstenS. The US does not use Imperial units. The US uses US customary units. Both Imperial and US customary units are derived from English customary measures, so there is a great deal of overlap, but measures like the gallon, quart, bushel, ton, and fluid ounce differ in amount, and the names and usage of units in the US and UK can also differ, e.g. stone is not used in the US, and survey feet are not needed in the UK. – choster Jul 1 '17 at 13:59
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    @choster I remember to having this discussion some time before, but forgot the accepted name of the US system. US customary units, then. – Thorsten S. Jul 1 '17 at 21:38
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    @JanDoggen 2015-12-06 fulfills the goal of removing ambiguity. – gerrit Jul 4 '17 at 18:53
  • @gerrit O, I get it, you and Thorsten mean to say that no-one would be so silly as to write yyyy-dd-mm. That seems a safe assumption – user40521 Jul 5 '17 at 13:42
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    @JanDoggen I always write dates as yyyy-mm-dd, as do all forms when I was living in Sweden. I don't see why it would be silly. I find it easiest to read too. But this comment thread is too small for a war of little-endian vs. big-endian; let's just agree that the American middle-endianness is the worst of both worlds. – gerrit Jul 5 '17 at 13:52

If "insist" means one more thing for curmudgeons to harass newbies about, I vote no.

That said, I really do wish people would avoid ambiguous formats.

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    Not at all, just simply means we can helpfully edit their post to the 'preferred' format :) – Mark Mayo Jul 3 '17 at 5:38
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    I don't think it is harassment. If the time of year for example affects the answer to the question and it is unclear, then it becomes impossible to give a good answer. – Communisty Jul 4 '17 at 9:50
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    Editing it to be unambiguous, and pointing out that it is ambiguous are not harassment. But I've often seen evidence that a few of us seem to take pleasure in harassing newbies for trivial matters. Most of us, fortunately, show that you don't hace to be a jerk to get quality. – WGroleau Jul 4 '17 at 11:51
  • Um, I think you got confused in your negations. "Avoid unambiguous formats" means that you want uncertainty. – Martha Jul 5 '17 at 17:10
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    I'm not confused, just my typing fingers. Wait, let's blame autocorrect. – WGroleau Jul 5 '17 at 17:45

I'd say 11.8.2011 (dd.mm.yyyy) is also unambiguous. It is commonly used in Europe. Or are there countries that use dots as delimiters like this with month and day reversed?

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    It is ambiguous. You want to infer an order based on the fact that dots are used. Is a reader from China supposed to know that and draw the same conslusion? – user40521 Jul 4 '17 at 9:49
  • It doesn't matter where the reader is from or what is their knowledge. If the format is not used in different ways elsewhere then it is unambiguous. Just like inches in the USA has always the same length regardless of the readers knowledge of the length of an inch. – Communisty Jul 4 '17 at 9:56
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    If it isn't ambiguous, why did you need to parenthetically explain it? Americans mostly use the slash (which looks like '1' in sloppy handwriting) but some use hyphen, space, or dot. And most assume the order is m.d.y – WGroleau Jul 4 '17 at 11:52
  • @WGroleau I thought I expressed my uncertainty to that question in my answer. I honestly don't know if some Micronesia happens to have the opposite expression. I'm happy to swallow my pride if someone proves me wrong :). – Communisty Jul 4 '17 at 11:57
  • You said it is UNambiguous. Is that what you meant to say? – WGroleau Jul 4 '17 at 14:32
  • Yes. Definition, by Merriam-Webster, is: not ambiguous. – Communisty Jul 5 '17 at 6:23
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    As others have noted, the nature of the delimiter used doesn't remove ambiguity: 11.8.2011 looks like November to an American, and like August to a European. Same goes for 11/8/2011, despite the fact that using slashes as the delimiter is not at all common in Europe. The only way for a date to be totally and completely unambiguous is to use letters, not numbers, for the month. (Unless of course you're writing in Lithuanian or Irish, in which case everyone will know what day and year you're talking about, but they'll have no clue which month it is.) – Martha Jul 5 '17 at 17:20
  • I don't disagree that using letters with months doesn't work. I'm saying that using dots with delimiters there is no question on what is the order of day, month and year (DMY). I've now even checked that there are no outliers from en.wikipedia.org/wiki/Date_format_by_country. I'm sorry that you Americans (read USA) have a hard time understanding this, but DMY is the most common order on earth and with dots as delimiters no one uses other than it. – Communisty Jul 6 '17 at 6:17
  • Here is a movie poster, showing that this format is indeed ambiguous. (Ignore which film the poster is for, it's the first I found.) – svick Jul 10 '17 at 12:55
  • Cursed shall be you Americans with thy inconsistent markings. – Communisty Jul 13 '17 at 9:41
  • @JanDoggen from China or not, no user should have problems to identify 4-digit part as a year. Then it is clear if it's gonna be read from right to left or from left to right... – Rg7x gW6a cQ3g May 29 '18 at 12:22
  • @svick it's a terrible example because a year is 2-digit so it's impossible to guess which part of it is a year. Only month is clear, because it can't be physically anywhere but between days and year, but where on hell a year has 20 or more months? – Rg7x gW6a cQ3g May 29 '18 at 12:24

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