Stamp catalogues are not entirely consistent in what they do and don’t list. This is especially the case in relation to what I shall call local modifications.
Our paradigm for a stamp issuing authority is a central government department which distributes standardised stamps to post offices under its control. A limiting case is the micro-state which has only one post office but we can safely ignore that.
In general, local post offices are supposed to use the stamps they receive in the ways intended by the centre. But quite often they do things to stamps before selling them, most commonly:
1. Perforating imperforate stamps
2. Bisecting stamps
3. Changing the face value of stamps invisibly
4. Changing the face value and showing the change with an overprint or manuscript note
5. Authenticating stamps at point of sale with a postmaster signature
6. Pre-cancelling stamps
7. Defacing stamps - for example, obscuring the face of a former national leader
This list is not exhaustive. In addition, stamps may be distributed not only to post offices but direct to government organisations or departments and they may mark the stamps in some way to prevent their theft and private use by employees. The marks are intended to ensure that the stamps are only used for official business. Quite often, the stamps will already be overprinted OFFICIAL or SERVICE when they arrive but, if not, local initiative might supply the necessary markings. This happened in India before 1900 though the stamps are quite rare unlike the regular On H M S and Service stamps.
In relation to any and every such modification, a central authority may require it, suggest it, tolerate it, forbid it. The actual situation may be unclear: when in 1920 the People’s Commissariat of Posts and Telegraphs instructed Russian post offices to sell Imperial kopek value stamps at x 100 face value, some regional stamp distribution offices and some local postmasters took this to mean that they should mark the stamps in some way to indicate the change. But many didn’t and re-valued the stamps invisibly. In contrast, when in the early 1990s Lithuania’s postal authorities instructed post offices to revalue stamps I don’t think any of them marked the change - the revaluation was always invisible.
When the stamps leave the post office some buyers may modify them before use. Common practices include:
1. Perforating imperforate stamps
2. Punching the stamps with company initials as a security device to protect against theft [Perfins]. In Imperial Russia, the practice was rare and, in practice, it is only stamps of the Russian Levant which are occasionally found with company perfins.
3. Overprinting or handstamping the stamps with a company name or logo likewise to protect against theft. In India, this was common until the practice was banned around 1900. At least one organisation - the Bombay Education Society Press - then responded by handstamping the gummed side of its stamps with its acronym B.E.S.P. So it was still the case that no employee could safely walk out of the office with mint stamps! Nineteenth century stamps from other British colonies (Ceylon, Hong Kong, Straits Settlements notably) are frequently overprinted with company cachets but in Imperial Russia it is rare and the cachets were normally applied after the stamp had been applied to the cover. Here, the motive seems to be to prove that a stamp was on the cover when posted, since if it is removed then the removal will be visible.
4. [Possibly - I have no examples] Gumming ungummed stamps in sheets to have them ready for use rather than using a glue pot at point of application to a letter.
Catalogue makers generally exclude these private modifications. As for the official or semi-official modifications, these are not treated uniformly though there may be some logic to the choice. Thus, the Departmental overprints of South Australia are listed in outline by Stanley Gibbons because the overprints were all done by the central authority. But the very similar Departmental overprints of India are not listed because they were local initiatives. When it comes to bisects, catalogue makers may try to distinguish those where official permission was granted to a postmaster (or an instruction given to all postmasters) and those where the postmaster took the initiative. If you had no phone or telegraph and had run out of stamps you needed, it made no sense to wait for a permission which might take a week or two weeks (or more) to arrive. From a philatelic point of view, that kind of unauthorised bisect is probably as interesting as the authorised one. It is only problematic if one suspects that the postmaster had been signed up by the local stamp dealer to create a scarce variety, as indeed has often been the case. In the Soviet Union by the 1930s and after, central control was very effective and local modifications by post offices very, very rare.
There is one interesting category which is not often noticed. Central authorities may damage stamps deliberately before issuing them, or may instruct postmasters to do the job. I know of two examples: in Hungary in the 1920s, sheets of stamps intended for post offices had some of the stamps in each sheet perforated before distribution with three small punch holes. The idea was to protect the revenues of the (hard currency?) philatelic department by making it unattractive to buy sheets of stamps at regular post office counters. Similarly, in the 1990s to protect a commercial monopoly of mint sales to dealers and collectors, the stamps sold at Turkmenistan’s post offices had perforations trimmed off on one side before sale. This has the curious consequence that you can only collect genuine postally used Turkmen stamps (rare in themselves!) if you are willing to collect damaged ones …
Locally modified stamps all have their specialist collectors and study groups; general catalogues could help by at least noting some of the more prominent local modifications. For example, postmaster and private perforations on the early stamp issues of Estonia and Latvia are common enough for copies to appear fairly frequently in old collections and on covers, often philatelic. The same is true for the 1917 imperforate issues of Russian Imperial Arms stamps. But in the case of the first post-1991 stamps of Lithuania, local perforations exist but are much less common and I guess many collectors would be surprised to learn that they do.