Reference For Faroe Islands Cancels On Stamps Of Denmark?

I just bought a 3-volume collection of (mostly 20th century) Scandinavian "town cancels", and contained in it is a fairly large section of Faroe Islands cancels on Danish stamps.

Are there any references available on these cancels/usages, or are they merely of nominal/curiosity value to collectors?

The 3 volumes in the collection are Sweden (I have the Facit cancel catalog), Finland (I don't have any reference for these), and Denmark (no reference for this area).

Thanks.

I think the Faroes didn't start issuing their own stamps until the mid 70's. I assume before that time Danish stamps were in use, hence the Faroese cancels on them.

There was one Faroes stamp issued about 1919; an overprint, I believe, of a Danish stamp. Several more issued in 1940 when the British occupied the islands to keep them out of German hands. Then issues in earnest in the 1970s.

For Faroe islands, there's a 1919 bisected stamp (a 1913 Danish 4 ore, blue),a 1919 2 ore overprint on a 5 ö Christian X green.
In 1940/41 the British Occupation Forces overprinted 5 Danish stamps with new values.
There were no further Faroe stamps until 1975, but Danish stamps used in Feroe are said to command higher prices, if you find someone interested on them.