Now Registered mail from Imperial Russia is common. But some Registered items are more unusual than others. And some things you will NOT find in the Imperial period, which ended with the abdication of Tsar Nicholas on March 2 1917 [ Old Style].
For example, the cover below is from post-Imperial Russia but maybe looks like it could easily be an Imperial period cover. There are two reasons why it cannot be that, apart from the readable date of 1918.
First, it is franked entirely with imperforate Imperial Arms type stamps which were only put into circulation during the period of the Provisional Government which came into being after the Abdication.
What about the second reason? Have a look. The cover is sent from ZELZAVA LIFL 17 1 18, addressed to Stomerzee where it was received STOMERZEE LIFL 17 1 18 - so a bit over a month before the German occupation of the Baltics. The cancellations look like standard late Imperial types
Keep looking. Answer below.