a few might be doubting that I don't care about rarity when it comes to covers :)
Since I buy a collection or 2 now and then, I sometimes find good items.
this service lettercard is an example of such. I knew it was a good cover, but it has a crease between 2 stamps so I can't use it.

At a seminar I met the leading exhibitor of Danish service stamps, and his jaw dropped while he said; this is 1 of, now, 3 known sent to a foreign country.
And while he browsed through my covers he told me that this also would have a much better life in his collection :)

Very late usage of service stamp, sent from the police, returned and unopened which is very rare, most likely one of a kind. Since it has a roller cancel I don't like I can't use it.
and I would happily swap these for some beautiful common covers as long as accumulated value match especially if these covers can add a ˝ point to an already incredible exhibition.
while I only hold on to aesthetic covers for my collection I'm not oblivious to value and rarity.