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Speaking about... GPT control numbers |
 ontrol numbers are very important to collectors of GPT cards. They have evolved over the years. The earliest Plessey cards, made in 1987, were promotional or demonstration cards. Some of these did not actually have control numbers but most had a control number in small blackish purple characters in the lower half of the card on the reverse. These, being black on black, can be difficult to see but the change in texture usually shows up quite clearly when the card is held at the right angle to the light. Some of the first control numbers, such as those on the Swedish and South African trial cards, consisted only of eight or six digit numbers or a single letter followed by a six digit number. But, early on, Plessey adopted the basic control number system which is still in use today. |
| Like the L&G optical cards the controls divide into a prefix and a serial number but, unlike the L&G controls, the country for which the card is intended is indicated while the date of manufacture is not. The controls take the form: Number. Three letters. Letter. Six digit number. An example might be 3JERD020542. The meaning of these are: |
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3 is the number in sequence of printings that have been done for that Telephone company. This card is from the third printing for that country.  JER defines the country or company - Jersey in this case. D distinguishes the specific card out of several which might have been done for Jersey in that printing. Usually a set of cards will have be lettered in increasing order of value and 3JERD is in this case the top value of a set of four cards - the 100u 'St.Helier at St.Aubin' of the Steam locomotives set. The lower values were, of course, 3JERA. . . , 3JERB. . . and 3JERC. . . 020542 is simply a serial number which is different for each card. |
 PT are generally very consistent in the use of this system. The first cards for a new telco will always have the controls 1ABC. . . regardless of whether those cards are demonstration cards, trial cards or for full public use. Thus 1SIG. . . , 2SIG. . . and 3SIG. . . were demonstration cards for Singapore and the first public cards had 5SIG. . . controls. So what happened to 4SIG . . . ? I have never seen a Singapore card with that control but GPT are generally consistent and I am sure it exists somewhere - almost certainly as another demonstration card. We have a similar puzzle with the first known cards of Montserrat where the cards have both a small notch (most of the other first Caribbean first cards which appeared at the same time had deep notches) and a control 2CMTA.... What happened to 1CMT ... ? Perhaps a demonstration card which has not yet come to light or, more likely a printing which had to be destroyed due to some error of design or function or which simply got lost.
One other factor has to be watched and that is the size of the characters making up the controls. These can vary from about 2.7mm. (on early cards) up to around 5mm and significant differences due to the use of different numbering machines can be found on otherwise identical cards. Many collectors try to obtain all known sizes for each card. |
 here followed a series of changes. The 'black on black' controls moved from the lower half of the card to the centre top where they have remained ever since. The next move was to make the controls much more visible by printing them onto a white rectangle and this was followed by controls printed onto silver rectangles. Both white and silver backgrounds are still in use and tend to correspond to two different printers to which GPT subcontract the production of the cards. All the early cards had seven ferrite bands on the reverse - three in line across the middle of the card and a short band in each of the four corners. It was then, in 1990, decided that the top two ferrite bands should be dispensed with and modern cards now have only five. |
       
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I have said above that GPT are consistent in their choice of controls and so they are for mainstream cards but this does not extend to the private cards of some countries. For Singapore and Malaysia, for  example, the normal three letter country designation is replaced by letters corresponding to the advertiser or sponsor. The initial letter is retained but the second and third letter generally reflect the sponsors initials. Normal Singapore cards have the control letters SIG as mentioned above but the many cards that have been sponsored by Fuji have SFU and those by NEC have SNE controls. Similarly Malaysia Uniphone normally has MSA but the advertising cards for Petronas have MPE controls. The GPT cards for Mercury, UK, however, had MER controls regardless of whether they are public or private cards.
New Zealand too has a somewhat idiosyncratic control numbering system. The early cards were perfectly well behaved with NZL controls starting with 1NZL for the trial cards in the usual way 2NZL for the First Issue cards, 3NZL, 4NZL and 5NZL for the Satellites and so on. The 1990 Christmas set however was of five cards with controls 6NZAB, 6NZBB, 6NZCB, 6NZLC and 6NZLD, presumably to reflect that fact that the first three were all of the same value, and this practice continued on later sets over the next year. The 1991 Christmas set saw yet another change of system with controls 101B, 102B, 101C and 101D where again the first two are of the same value The Antarctic set issued in February, 1992 reverted to the 1991 system while the Summer Sports set in March, 1992, had 111B, 112B, 111C, 111D and 111E, the Winter Sports set in June, 1992 had 113B, 114B, 112C and 112D and the Hedgehog set of August, 1992, had 121B, 122B, 121C and 121D. While one can see some sort of a pattern here, the logic is not self-evident.
Text by Steve Hiscocks.
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There has in fact been a trend towards eccentric control numbering systems with encoding, and hence numbering, taking place in the country of use rather than that of manufacture. Thus Saudi Arabia, in compliance with Saudi law, now encodes its own GPT cards and applies the control numbers, and Sapura in Malaysia does both its own Uniphone cards and those of Vietnam which are provided through Sapura.
ll of the above comments relate, of course, to cards as they are produced by GPT. The situation can become confused when telcos take to overprinting excess cards of one design with a new design. Mercury, UK, which has now ceased to issue cards, acquired the technology to take the design surface off cards leaving a matt black surface for reprinting. This had several interesting effects. The numbers of cards of the types so processed were reduced from the numbers originally printed and listed in the catalogues. Controls previously associated with certain cards appeared on new cards and new cards appeared with a wide variety of controls on any one design. One card featuring an Airedale dog, of which only 1000 were printed, occurs with no less than six different control prefixes and a single card with a deep notch! New Zealand also took to overprinting older cards but without taking off the old design first. This not only gives rise to anomalous controls but also to cards which have to be handled with great care if the new design is not to be damaged! 
