In many of my posts I will include composition dates for particular works. These dates will be based on the best information I can find. Quite often a composer will spend several years on one particular composition, or the specific date of completion is not know, but other dates concerning the piece are known. As such, I will cite the date when the composition was either 1) completed, 2) first performed or 3) published, in that order and depending on what information or additional information is available.
Quite often it is unknown when a piece was composed. In this case I will indicate so, or I will indicate the composer's birth date and date of death if known. The purpose of providing a date is to give the reader some idea as to when a composition was written for purposes of comparison with music from various eras. However, I welcome any new information on dating or other aspects of a particular composition or composer; provided that a reader can cite reliable documentation. In such cases I will try to update posts, which feature that information.
While I often refer to Wikipedia and other online encyclopedias, these should not be cited as authoritative, since their articles can be edited by people who have limited credentials - although I may initially refer to their dates and information if I can't find other sources. I recommend following their external links for more reliable sources, or referring to other published sources either online or in printed form.