What is rare?

As you gradually grow older and rack up more years of experience you do get a more informed view of which things are rare. You notice that some things pop up with some regularity and other things don't.

As a collector of Siberian Civil War stamps and postal history there are a few prime candidates for rarity. I'll disregard the Nikolaevsk-on-Amur garbage, but for example, the Merkulov Anniversary issue of 1922 is hard to find. About 2000 sets were overprinted and it can take a few years before you're lucky enough to find a set. Of course, these days the internet improves your chances of success dramatically!

Mint, these stamps are hard to find. Postally used, these stamps are downright rare.Disregard the philatelic postmark of Vladivostok "g" and you really have to get lucky to find used stamps of this set.

These stamps on cover? Yikes! I've seen about half a dozen covers over the years. Most of these were philatelically-inspired. Good luck!

The low print run is somewhat deceptive in this case. Sure, only 2000 sets were issued but these all seem to have ended up with a small number of stamp dealers and collectors, ensuring a high survival rate over the years.

Other stamps may have had larger print runs but present different problems. Take the 1 rouble imperforate of the DVR Monogram issue. 3000-5000 were issued, depending on which source you believe, so that doesn't make them that hard to find, compared to some of the stamps with smaller print runs. Postally used copies to turn up - one wonders where they came from?

But on cover?

You need to get very very lucky to find these stamps on cover, and you're not helped by the odd fact that almost no parcel cards or money orders are known from the Vladivostok area from 1918-1923, since those are usually a good source of postally-used high values.

9-fold weight registered letter from Vladivostok to USA

This cover is one of very few that I've seen, and the only one with a single franking. It also appears to be non-philatelic. In 27 years of collecting that makes it the only one I've ever seen. Rare!