see <#edu=Earliest Documented Use>.

see <#efo=Errors, Freaks and Oddities>.

see <#eku=Earliest Known Use>.

the earliest date on which a <#stamp> or item of <#poststa=postal stationery> is known to have been used, as documented by expert opinion.  Generally applied to items issued in the nineteenth and early twentieth centuries that did not have formal <#firstdayofissue=first days of issue> and that might have arrived at different post offices at different times.

the earliest known date on which a stamp is used, even if prior to the official <#firstdayofissue=first day of issue>.  Generally applied to contemporary stamps.