I'm constantly debating with myself whether certain stamps are worthy of inclusion in my stamps on stamps collection or not. These two lovely sets from Great Britain are good examples. The first set is not stamps on stamps, but rather basic stamp designs on stamps, which is not the same thing. There are no signs of the actual stamps those heads are supposed to adorn. The second set is only new designs imposed on old.
I have many other doubtful stamps on stamps. For instance illustrations of stamp collecting with stamps that are so small and blurry that they can't be identified. Or simply reproduction of old stamps with only the denomination changed. I will come back to more such doubtful cases another time. Still, when they look as good as these, I find it quite appropriate to make some space for them here.