Cosmo,
Please read these links regarding the use of Mayday and Pan, one is from the FAA the other from the CAA (UK.) Your view of the limitations of each phrase don't seem to be represented here. Also please note there is no reference to any form of 'declaration.'
http://www.faa.gov/air_traffic/publi...m/aim0603.html
http://www.atac.ca/web/images/Docume...al%20Pilot.pdf