What does a letter mean at the end of a Madrid registration number?
A few international registration numbers end with letters of the alphabet. See for example LUSTCRU which has an international registration number ending in "A". What does that letter mean? The answer may be found at Madrid Administative Instructions, Part Six, Section 16, Numbering Following Partial Change in Ownership:
a) Assignment or other transfer of the international registration in respect of only some of the goods and services or only some of the designated Contracting Parties shall be recorded in the International Register under the number of the international registration of which a part has been assigned or otherwise transferred.
(b) Any assigned or otherwise transferred part shall be cancelled under the number of the said international registration and recorded as a separate international registration. The separate international registration shall bear the number of the registration of which a part has been assigned or otherwise transferred, together with a capital letter.
A kind person at WIPO tells me that so far it has gotten as high as the letter "I", as may be seen in international registration number 230562.