The official posthorn FDC issued by the Post Office has a variant with a large posthorn. This cachet is a standard PO cachet used on local Post Offices and has been seen on several FD issues. This variant was observed also with the Salvation Army stamp from 1995 issued with a local PM (Saudarkrokur). It even contained a 4 block of the SA stamp!! It is very rare to see 4-blocks on the Icelandic SA FDCs!
Another unlisted FDC on a puffin cachet has also been found with a local PM from Vigur.