I'd suggest this thread primarily as a source of ID
of the numerous shards of cut paper
we receive back of book as floorsweepings.
If anyone specialises in stationery of the various countries
and can ID them, please contribute.
Unknown:
thick board: postcard

Thick board: writing on back:postcard

Thinner paper : cannot be postcard or stamp
Newspaper wrapper?

thick board: swiss postcards?

