Most serious collectors now start from John Bulat's Catalogue, published in 2003 but based on a manuscript worked on for decades previously. Leave aside the many typographical errors and there are three main areas worth thinking about.
First, the very different treatment of Trident overprints and West Ukraine overprints.
For Tridents, excepting one or two isolated instances which may be mistakes, Bulat goes up to valuations of $300 after which he makes frequent use of the - - system to signal "Too Rare to Call". Bulat's[ $ ]300 is simply Dr Seichter's top value of 600 [ DM ] in his 1966 Sonder-Katalog, divided by two. After that, Seichter also uses the - - system.
But for West Ukraine, Bulat goes up to $30 000 and makes very little use of the - - system.
Now if we simplify and reckon Bulat's lowest price as $1 for both Ukraine and West Ukraine, we have a range for West Ukraine 100 times wider than for the Tridents.(* See footnote) Why? It's certainly not because of rarity: many Tridents are as rare as the rare stamps of West Ukraine. It's certainly not to do with marking down "philatelic" productions - with the exception of the Kolomyia Registration stamps, the stamps of Western Ukraine are all philatelic productions. It does have a lot to do with prices which can be achieved: Bulat's $30 000 was comfortably exceeded in the Zelonka sale for the stamp to which it relates (Bulat # 65) and no Trident stamp has recently sold in widely-advertised auctions for even 10% of that and very few for more than 1%.
As far as Tridents are concerned, the current position is very much like that for Zemstvos before the Fabergé sale of 1999. Before then, no one would pay more than a few hundred dollars for a single Zemstvo stamp. That ceiling has now been completely removed. The Trident situation will only change when collectors realise that the ranges 1 - 300 and 1 - 30 000 are pretty much self-fulfilling prophecies.
Second, the validity of relative valuations
In valuing Tridents, Bulat closely follows Seichter, generally dividing by two. Now Dr Seichter was valuing Tridents as far back as 1940 when he published his Spezialliste der Briefmarken der Ukrainischen Volksrepublik. Basically, the relative valuations we use were established over 70 years ago. That means that they take no account of (1) destruction and loss, which is never even-handed, whether it results from war, flood, fire or collector carelessness; (2) discoveries in archives or dealer remainder stocks or collector hoards - things which are also not likely to be balanced. As a result, we all have the experience of being able to obtain stamps with high Bulat valuations quite easily and other ones with low valuations with great difficulty. After 70 years, it is time to examine the relative valuations again. To give just one example, though the Zelonka sale has released some onto the market, just try finding the Kyiv 1 Special Types (Bulat 109 - 45) even those with valuations below $10. (And just in case you ask, I have none in stock).
Third, the relation of a Bulat $ to an actual price
Here there seems to be a divergence between Europe and the USA. When we are talking about individual Retail prices (for example, for stamps on a Wants List), American collectors are still hoping to pay about 50 cents for a Bulat dollar and sometimes they may find stamps at that price. Collectors in Europe are willing to pay more - a dollar or sometimes a €uro for a Bulat dollar - and so in Auction they are more likely to take the choice items. In my experience, most of the really common stamps (under 50 cents in Bulat) remain so common that no one should pay more than ten or twenty cents for them. But once you get above something like Bulat $10, there are many hundreds of listed stamps which are actually quite hard to find and where a real dollar for a Bulat dollar is a bargain.
* Bulat goes down to 10 cents for Tridents and 25 cents for Western Ukraine, so technically the range is much wider. (I am struggling with the maths!)