The primary worldwide catalog of UPU International Reply Coupons (IRCs) is Yao's Catalogue of Worldwide Reply Coupons, Volume I: The UPU Coupons, published in 2017. The catalog is completely sold out and quite difficult to obtain; I found out about it too late and then it took me two years to find a used example for my own use. Work on a new edition is said to be underway, but I do not have any information about a potential publication date. I do not know of any other modern catalog listings of only Danish IRCs.
Danish IRCs are seldom offered. I am always interested in buying Danish and all Scandinavian IRCs, as well as groups and collections of IRCs from all countries. If you are seeking Danish or other Scandinavian IRCs, please let me know -- I usually have more IRCs in stock that are not on the website.
International Reply Coupon (IRC): 1929 Type (London UPU Congress 1929). "DANEMARK - DANMARK" printed in blue and denomination "50 ØRE" printed in blue. This type does NOT have "C22" printed on it anywhere. The watermark consists of one large double-line-letters "UPU". Backside text is in: German (gothic lettering), English, Spanish, Italian. This example was sold and postmarked on left side at "KØBENHAVN 18" 2 June 1948. This is in "Mint" (NH) Postmarked VF condition and was never redeemed for stamps to mail a letter. (If it had been redeemed to mail a letter -- thus "Used" -- there would be another postmark, on the right side.) Danish examples of the 1929 Type are remarkably hard to find!
ACTUAL item.
Reference
For reference only. NOT for sale.
247701
International Reply Coupon (IRC): 1929 Type (London UPU Congress 1929). "DANEMARK - DANMARK" printed in blue and denomination "50 ØRE" AND OVERPRINTED "70 [four wavy lines]" in blue. This type does NOT have "C22" printed on it anywhere. The watermark consists of one large double-line-letters "UPU". Backside text is in: English, Arabic, Chinese, Spanish, Russian. This example was sold and postmarked on left side at RINGSTED, 19 August 1950. This is in "Mint" (NH) Postmarked VF condition and was never redeemed for stamps to mail a letter. (If it had been redeemed to mail a letter -- thus "Used" -- there would be another postmark, on the right side.) Danish examples of the 1929 Type are remarkably hard to find!
ACTUAL item.