Do not place this template in any Citation Style 1 citation's |year= parameter. All text in |year= the parameter is made part of the citation's COinS metadata. The |year= parameter should include year data only.
Do not remove the template without fixing the problem one of the following ways.
If you know the year (or year range in some cases), fill in the needed information, and remove the template.
For a template-formatted citation, there are three basic ways to do this:
|year=YYYY
or, if you know the full date and the template does not expect a |year= value specifically, then specify it using |date= and whatever date format the rest of the article uses:
Some publications use some other kind of date range, such as a season or whatever:
|date=Winter 2009/2010
For a free-form citation:
Just add the year (or range, or more specific date) as appropriate to the format of the citation; or...
Better yet, convert the entire citation to {{cite journal}}, {{cite news}} or some other {{cite xxx}}-series template, as appropriate for the work in question.
If you know that no year was specified by the original source, as is common on many Web pages, you have several options, listed here in order of preference.
Use the copyright year (or year range) if one is specified, and use [square brackets] to specify that this is what it is:
|year=2006–2010 [copyright date]
Failing that, for non-news sources, use the year from the page's last-modified date (use your browser's "get page info" type of command; for example it is "Tools > Page info" in Firefox on Windows); only use this date if it is plausible (many sites always show a very recent last-modified date because of dynamic content updating such as sidebar ads.
|year=2003 [last updated]
This solution should never be used with news journalism, as it is closely tied an event's specific date, the accuracy of which is important for placing such a source in proper context.
Another option is an estimation, if you have reason to know approximately when something was published (i.e., you are better than guessing):
|year=ca. 2009
Finally, explicitly state that the year was unspecified if none of the above are practical (it will appear inside parentheses in most citation templates, but if it does not it should probably be put in [square brackets]):
|year=year unspecified
or
|year=[year unspecified]
For free-form citations:
No year specified.
Do not use question marks.
Do not leave the information blank and untag it, or someone else will just come along later and flag this with {{Year missing}} again!
Do not use |year=none, |year=unknown or anything else vague; any implication other than that the source itself did not specify a year is simply a signal to other editors to re-tag it with {{Year missing}}.
If you don't know:
Check the source, and add the necessary information, as above.
Do not use question marks.
If the source is a dead link, check archive.org for a backup copy (see your {{citation}}/{{cite xxx}}-type template's documentation for use of |archiveurl= and |archivedate= parameters). If no archive copy is available, use {{Dead link}} after the citation, but leave {{year missing}} as well.