Transient province: Odessa Guberniya

These days, Wikipedia is a very useful reference for something that used to be almost impossible to keep track of: changes in the provinces of Russia/USSR. There was a lot of restless tinkering with guberniya borders during the Imperial period but it wasn't until the 1920s that large-scale change became common, making it hard to keep track of what province any particular city might be in.
Odessa guberniya is a great example. There was no such animal in the Imperial period, Odessa being in Kherson guberniya, but in 1920, Odessa guberniya was created during the split of Kherson guberniya (the other bit becoming Nikolaev guberniya). It lasted until 1925 when all guberniyas were abolished and the map of the Ukrainian SSR was redrawn, in okruhs this time, so Odessa guberniya became Odessa okruh. That lasted until 1930 when the okruhs were abolished and everything went to oblasts, so we got Odessa oblast'.

Attentive postmark collectors can actually track this process in postmarks, although the postmarks did sometimes lag after the reorganizations. The card below shows a nice bilingual postmark from the Odessa guberniya period, from a place called Bilyaevka. I'm sure there are lots more but I rarely see them.