Vehicle registration plates of Luxembourg

Vehicle registration plates in Luxembourg bear a maximum of six characters. The standard series in use today uses a format of two letters followed by four digits (e.g., XY 3456). Marks consisting of four or five digits and no letters are also issued.
The numbers are issued at a national level and give no indication of regional origin. Plates have black characters on a yellow background, with the standard blue EU stripe on the left. The current usage and format of plates was enacted by parliament in June 2003.
Standard plates.
The two-letter/four-digit format follows a rather unusual scheme, detailed below. The apparently random order of issue makes it difficult for the uninitiated to determine a car's age from its number plate. Leading zeros are used on car number plates but small vehicles such as mopeds have miniature number plates showing only two letters and two digits.
Custom plates.
Custom plates conform either to the standard format or consist of four or five digits. The scarcity of four-digit numbers means that there is a waiting list for them. Obtaining a custom plate costs €50. A custom plate can be issued only for new cars or upon a change of ownership. There is no market for trading numbers privately.
History.
Plates originally comprised digits only. (Four- and five-digit numbers can still be issued on request, but lower numbers are withheld from private use once the car is taken off the road.)
More recently, combinations of one letter and four digits, then two letters and three digits, were introduced, but these are no longer issued and are therefore gradually disappearing. The rear number plate latterly featured a large EU flag without a country code.
A new registration number is allocated each time a car with a number in the old format changes ownership.
Plates used to have white numbers on a black background, but these have all but disappeared with the exception of classic cars, for which there is a special exemption.
Sequence.
The order followed by the standard series letters and digits is rather unusual - numbers below 4000 are reserved for custom plates: those from 4000 to 9999 are assigned in blocks of 1000 with a changing sequence of letters. The series set out by the legislation was BA4000-BA4999, CA5000-5999, DA6000-DA6999, etc. However, it would appear that the issuers of the numbers took a while to adopt this, as the CA series used 4000-4999 before DA followed with 5000 to 5999.
The prescribed sequence of issue follows a pattern of ascending and descending alphabetical order of the two letters, as can be seen in the following list. When the first block of 1000 AZ numbers has been issued, we will presumably see the issue of BA5000.
Note that certain letters (I and O) and combinations are excluded. The list should be read from top to bottom, left to right: