I've been doing a bit of research on the Dutch stamps for the International Court of Justice in The Hague, which have been issued ever since the 1930s. The early ones, up to the 1950s, consisted of current stamps with an overprint in gold.
I was bascially wondering whether they were more gimmicks rather than properly used stamps. I was wondering that because the current issue denominated in euros has not kept pace with the rate changes, so basically there is now no stamp for the basic inland rate, because that changed some years back from 39 to 44 ct.
I've been looking for ages to find any material to show that these stamps were really used, but had basically given up, expecting I'd have to settle for just mint stamps, and cancelled to order copies of the older ones. Mint stamps were not made available in the old days, although some did end up on the philatelic market, like this 1950s stamp with the Peace Palace on!
But thankfully, two auction catalogues appeared at the same time, both advertising properly used Court stamps on Court envelopes! So I'm happy to be able to show you one!