In the case of cancelled Pakke-Porto you can only be absolutely shure that they were postally used
if they are on Postal Clips or Adresskort.
KGH have the advantage that they are less spectacular and therefore cheaper.
Especially in the first years there are many different types ( which are sometimes also quite expensive ).
Another advantage is for me that they ( this is not valid for the new ones ) are less
likely to have been produced for collectors use.
It needs to be emphaized that date cancels without readable year or >1938
are cancelled to favour. There exist also many CTO ( cancelled to order ).
It was possible to obtain several KGH-Cancellations in Kopenhagen. For K3.4 this was possible
until 1953 ! Also K0.5 could be obtained until 20 years after official use ( until 1928 ! ).
Greenland-Cancellations are rare and expensive. It is important to know that a big part of these stamps
come out of the Avane-System or were cancelled for collectors use ( see Egedesminde ).
Stamps on brown paper as used for parcels always need to have the cancel connect the stamp with the paper
and the fare making sense ( which is not the case in the Egedesminde ). Genuine Postal Clips are very rare and expensive
and need to have a certificate.
Adresskort are very interesting and expensive. Prices from about 200$
Cancels are always an uncertainity and should ( unless there is a certificate ) not be paid too much for.
The prices are unfortunately often very high and near catalogue prices. Good possibilities are sometimes at ebay, Scanphil, Norsten etc. I have also some 2. quality ( thins, tynd plet ) from Hoiland that were reasonably priced. Less beautiful cancels are also more likely to be genuine than exeptionally nice ones ( which collector or dealer will ask for lousy cancelled stamps in the post offices ). With unused stamps the mint version is usually half the price or even less ( I collect front sides, not back sides ).
With good knowledge of Pakke-Porto there are sometimes possibilities to make real bargains.
I bougth both my Nr.1 for something like 10$ as Nr.4 on ebay. No one had realised that they were in fact
Nr.1a with perforation 11.70x12.15 :-)
My 3Bd was sold to me as Nr.7 :-)
All my Nr.16 with K3.6 ring cancel were sold to me as Nr. 9 :-)