Is it postal stationery?

Chile 2004 Official Envelope

Starting in 2002 Chile has released stamped envelopes for Christmas, Mothers Day, and Valentines Day which have been sold at the post offices with prepaid domestic postage. The value is not indicated on the envelopes but various markings indicating "prefranquero" (prepaid) have been used.  All of the envelopes come with a matching sheet of paper for the message.

The 2003 Valentines Day envelopes had the prepaid marking added in black. It looks as if it was applied by a machine similar to a meter machine.

The 2004 Mothers Day envelope used the same device but this time the color is red.

In June 2004 an envelope was used using the same "prefranquero" device in black that promotes the new parcel service for members of the military and their family. The usual matching sheet describes the new service.

This envelope was not sold to the public but used by the Chilean government..

Is it postal stationery? Should it be treated as an official envelope? The "prefranquero" marking is exactly the same at the 2003 Valentines Day "prefranquero" marking.