The (alpha)numeric part of a registration number format in certain countries can be variable. For instance, for Bulgaria, the prefix is BG. However, depending on the organisation, 9 or 10 numbers can be put behind.

Due to the above, no format can be configured for VAT numbers within such countries. Bulgaria is not the only country; dozens of countries have the above requirement. There should be a possibility to make the (alpha)numeric length of a registration number variable, however, to require a fixed prefix (in the case of Bulgaria BG)