All serious collectors of Russia know about the celebrated 'Stamps of the Russian Empire Used Abroad' series authored in the late 50s by Simon Tchilinghirian and William Stephen and published by the British Society of Russian Philately.
Released over six volumes it is, still today, the reference opus for Russian stamps and cancellations in China, Levant, Mongolia, Sinkiang, Bukhara, etc.
When the first installment was published in 1957, almost nothing was avalaible on the subject. No man's land. It was a stunning ground breaking work, for which we can be very grateful for. Thanks to it, some collectors started to dig more deeply into their own collection, while others extended their area of interest.
Certainly, one of the main benefits of this publication has been to raise dramatically the awareness among collectors. There was, at least, a basis upon which everyone could now exchange and discuss, a common alphabet to the same language. As a result of this effervescence, some addendas were regularly published, essentially in the British Journal of Russian Philately. Noted contributors were Michel Liphschutz or Igor Maslowski, to name only a few.
This reminder of the past is important to understand today's value of this work. As well as its current's weaknesses.
Those weaknesses are two fold. First, since the last 40 years, a huge amount of discoveries has been made. Previously unrecorded material, that was unavalaible to the authors, has surfaced on the market, been expertised, been published (or not). This is the main factor that determines the -important- limitations of that work today. Simply put, you cannot trust anymore T&S's listings, and especially the scarcity ratings, as so many new discoveries have definitely changed the face of the game. The second fold is more tricky. The authors, in some places of their work, have presented some personal interpretations or guesses as definitive statements. But you cannot change facts and history. In the late BJRP, Dr Casey has skillfully demystified some of them, I leave the reader to this excellent research work to get an idea of what I mean.
I will give two examples of my own regarding the scarcity ratings. Below is a cover in my stock from the Russian Post in Bukhara, franked with a 7 kopecks Arms (1889 issue). The scarce cancellation from Bukhara's PO (struck once on the front, and cancelling the stamp on the back) is recorded in T&S Volume 3, figure 354. It is described as 'RR' (yes, it stands for 'very rare') on all stamps of this issue. But the fact is that today there are, at least, a few dozens of those covers. I would therefore not rate this -nevertheless scarce- cover as 'RR', not even 'R'.
The second random example concerns the Russian Post in China. If you look closely at T&S' CER offices listings & ratings, and compare them to what has been discovered since, then you would better start from scratch again. I blogged last year about a rare Fulya Erdi postmark, recorded in T&S Volume 5, page 419. In 1958, only one loose stamp was known, and this small station was rightly rated 'RRR'. 54 years later, there are at least 8 to 10 covers and cards recorded, as well as numerous pieces, making the rating drop from RRR to R (or RR at best).
With those considerations in mind, I strongly recommend Tchilinghirian & Stephen 'Stamps of the Russian Empire Used Abroad', if you didn't get it yet. The Rossica Society and BSRP have re-edited that opus last year on digital format, and you can now get the six volumes sent directly at your place for the (ridiculous!) price of 45$, while helping at the same time a well-deserving philatelic society: you can order your copy here.
The classic works of pioneers are like trampolines; they give a powerful base upon which its own flexibility (imperfection?) allows the next generations to reach higher levels. So, thank you, MM. Tchilinghirian & Stephen!