The previous system used numbers with two parts, a letter and several digits. The letter is first letter of the surname. While usually obvious, prefixes such as de or von, and titles such as Füerst or Prinz are not counted. The prefix Van usually has been counted, von has not; it's not entirely clear what the logic is here. The letter is followed by a number, which is assigned in sequential order to the extent possible (but see below). Members who left before 2022 will retain these numbers.
In the above system, members whose last name changes (''e.g.'': a woman changing name at marriage or divorce) were not issued a new membership number.
An earlier system of sequential numbers exists, and these are being loaded into the Membership Book by prefixing them with "X-" (as no surnames in the second system began with that letter).