Monochrome collection with multiple franking
Multiple franking is often spectacular.
Many collectors will pay particular attention to such items. This is particularly the case in Germany and in the German-speaking countries but also in Anglo-Saxon countries. Thus the Michel Catalogue rating this type of postage usually gives important added value. It is all justified more easily that finding this kind of documents is sometimes very difficult.
Multiple franking, means a composition of a single value, stripes, blocks or more isolated copies of the stamp, without the addition of other values (in this case one speaks of mixed franking whose value, unless facing an exceptional postal rate, are much lower).
To give a hint of scarcity, you should know that it is necessary to handle hundreds of letters to hope to find one, and I am far from exaggerating. It is necessary to be armed of a lot of patience to find some.